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FHWA Home / Safety / Speed Management / Traffic Calming ePrimer

Traffic Calming ePrimer – Module 3

3.9 Roundabout

DESCRIPTION AND GENERAL PURPOSE

A roundabout is an intersection design that contrasts with designs that require traffic signal control or stop control. A roundabout is often used as a replacement for a signalized intersection. A small modern roundabout and mini-roundabout are similar (presented as a separate traffic calming measure in section 3.8 of this ePrimer [provide link]).

A full roundabout is typically appropriate only at the intersection of two arterial streets or of an arterial street with a collector street. The full roundabout does not generally fit within the footprint of lower classification street intersections.

A roundabout is sized to accommodate all large vehicles circulating the center island and the center island is non-traversable.

A roundabout provides a horizontal deflection with an island at the entry point and requires every vehicle to follow a circuitous path no matter which departure leg of the intersection is the destination (as illustrated in Figure 3.9.1). As a result, traffic speeds are moderated (note: even though overall delay per vehicle may be reduced in comparison to a signalized or stop-controlled intersection).

The roundabout is included as a traffic calming measure in this ePrimer because it can be used to change the operating character of a roadway as it transitions from a higher-speed operation to a lower-speed operation within a higher-density community with more pedestrian presence.

The reader is referred to NCHRP Report 672, Roundabouts: An Informational Guide for a thorough description of roundabout characteristics, applicability, effectiveness, and design issues.

Figure 3.9.1. Single-Lane Roundabout. The figure contains an overhead photograph of a single lane roundabout. The splitter islands are green and red. The roundabout contains a tower surrounded by low bushes. Two pickup trucks are using the roundabout; one waiting to enter and the other in circle.
Figure 3.9.1. Single-Lane Roundabout
(Source: Omni-Means, Ltd.)

APPROPRIATE APPLICATION

Appropriate Application – Roundabout
Type of Street Appropriate for the junction of arterial streets and of arterial streets with collector streets10
Intersection or Roadway Segment Applicable only at an intersection

Can be used to realign a closely-spaced offset intersection into a single intersection; if intersection remains offset, roundabout can be laid out in the form of a "dogbone-shape" design
Roadway Cross-Section Can be used at intersection of both one-way and two-way streets Approach legs can be multiple lanes

Preferable to have an urban cross-section (i.e., curb and gutter) like that shown in Figure 3.9.2

Can be applied on a cross-section both with and without a bicycle facility; bicycle lane not striped within a roundabout

Can be applied along a roadway with on-street parking
Speed Limit Can accommodate any typical urban operating speed
Vehicle Traffic Volume Can be appropriate at any level of traffic volume; multi-lane modern roundabout can be effective at daily entering volumes up to 60,000
Emergency Route Can be appropriate along primary emergency vehicle route or street that provides access to a hospital or emergency medical services
Transit Route Can be appropriate along a bus transit route
Access Route Can be appropriate along a primary access route to commercial or industrial site
Grade Can be installed on a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided

Maximum grade should comply with local standards and criteria; as an example, Portland OR limits longitudinal street grades at a roundabout to 10 percent

10 A mini-roundabout or traffic circle should be considered for the intersection of lower-classified roadways

Figure 3.9.2. Roundabout with Urban Cross-Section (i.e., Curb and Gutter). This figure contains a photograph of an entrance/exit for a roundabout. A car enters it on the right hand side. It is separated from a car exiting the roundabout by a splitter island. Trees and other landscaping can be seen in the center of the circle.
Figure 3.9.2. Roundabout with Urban Cross-Section (i.e., Curb and Gutter)
(Source: James R. Barrera)

EFFECTS AND ISSUES

A complete description and discussion of the effects of a roundabout on mobility and safety is presented in NCHRP Report 672, Roundabouts: An Informational Guide.

ADDITIONAL DESIGN CONSIDERATIONS

A complete description and design considerations for a roundabout is presented in NCHRP Report 672, Roundabouts: An Informational Guide.

The MUTCD has sample striping layouts for single, multi-lane, and hybrid roundabouts.

3.10 Speed Hump

DESCRIPTION AND GENERAL PURPOSE

ITE has developed a recommended practice entitled Guidelines for the Design and Application of Speed Humps. Further guidance and clarification can be found in that publication.

A speed hump is an elongated mound in the roadway pavement surface extending across the travel way at a right angle to the traffic flow (see Figure 3.10.1). A speed hump is typically 3 inches in height (with applications as high as 4 inches) and 12 feet in length along the vehicle travel path axis (note: a speed hump that is 20 feet in length and flat in the middle is considered a speed table in this ePrimer).

At typical travel speeds along a residential street or in a small commercial business district, a speed hump produces sufficient discomfort to a motorist driving above the speed hump design speed to discourage speeding. It encourages the motorist to travel at a slow speed both upstream and downstream of as well as over the speed hump.

[A speed hump is also referred to as a road hump or undulation.]

[What's the difference between a speed hump and a speed bump? A speed hump is typically 12 feet in length (in the direction of travel), between 3 and 4 inches in height, and is intended for use on a public roadway. A speed bump is much shorter, between 1 and 2 feet in length (in the direction of travel). A speed bump can be as much as 6 inches in height. A speed bump is typically found in a parking lot or commercial driveway, but not on a public roadway.]

The initial speed hump applications were similar to the 12-foot speed hump, characterized in this section of the ePrimer. Variations in length and shape were applied and were initially considered speed hump variations. As the 20-foot measure became a standardized size and shape, it became known as a speed table. The reader is cautioned that when reviewing literature, design standards, and effectiveness analyses for speed hump, what is included within the umbrella of "speed humps" has varied over time.

[Five field studies of 51 speed humps measured crash reductions between 33 and 48 percent (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Crashes, July 2014) http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_crashes.cfm]

[Seven field studies of 199 speed humps measured reductions between 6 and 13 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014 http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_speed.cfm]

Figure 3.10.1. Speed Hump with Bicycle Lane and On-Street Parking. The figure contains a photograph of a two lane road with a bicycle lane and on-street parking. A bicyclist in the bicycle lane is moving away from the photographer and approaches the speed hump, a raised portion of pavement painted with white angular lines. Cars and trucks are parked in a parking lane on the right hand side of the road.
Figure 3.10.1. Speed Hump with Bicycle Lane and On-Street Parking
(Source: Scott Batson)

APPROPRIATE APPLICATION

Appropriate Application – Speed Hump
Type of Street Appropriate for a residential local street or any street where the primary function is to provide access to abutting residential property (see Figure 3.10.2)

Appropriate for a street that provides access to a school, park, or community center

Also appropriate for neighborhood or residential collectors
Intersection or Roadway Segment Placed at a midblock location, and not near an intersection; as an example, Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 feet from a signalized intersection

Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet (see Figure 3.10.3)
Roadway Cross-Section Can be used on a single-lane one-way street or two-lane two-way street; should stretch across only one travel lane in each direction

Typically installed on a roadway with an urban cross-section (i.e., curb and gutter)11

Typically placed one foot from a curb for drainage or six inches from the edge of a non-curbed roadway

A speed hump can be applied on a cross-section both with and without sidewalks or bicycle facilities
Speed Limit Appropriate if posted speed limit is 30 mph or less (per ITE Guidelines for the Design and Application of Speed Humps); many jurisdictions adhere to ITE maximum (e.g., South Carolina, Pennsylvania); some use a 25 mph ceiling (e.g., Delaware)

Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume Appropriate if daily traffic volume is relatively low; as examples, Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; Pasadena, CA (41) uses a daily volume maximum of 4,000, with at least 1,000 vehicles in each direction

ITE Guidelines for the Design and Application of Speed Humps recommends consideration only if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route Generally not appropriate for a primary emergency vehicle route or a street that provides access to a hospital or emergency medical services; speed cushion and speed table are similar vertical measures that could be appropriate

An emergency vehicle can cross a properly designed speed hump but at a slow speed
Transit Route Generally not appropriate for a bus transit route but examples of speed humps on bus routes do exist; a speed table and speed cushion are similar vertical measures that could be appropriate
Access Route Not appropriate along the primary access to a commercial or industrial site
Grade Can be installed on, or beyond, a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided

ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a grade of 8 percent or less (see Figure 3.10.4); many jurisdictions adhere to that maximum (e.g. Pennsylvania, South Carolina) but others follow a lower value: Delaware – 6 percent; Minnesota and Pasadena, CA -5 percent

11 If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be necessary to discourage a motorist from driving around the hump. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

Figure 3.10.2. Speed Hump on Residential Neighborhood Street. This figure contains a photograph of a street in a residential area. A speed hump is marked by a yellow diamond sign and painted white angular lines. A painted bicycle icon and arrows are painted on the street just before the hump.
Figure 3.10.2. Speed Hump on Residential Neighborhood Street
(Source: Lucy Gibson)

Figure 3.10.3. Speed Hump Along Horizontal Curve. This figure contains a photograph of a curving two lane road divided by a double yellow line in a wooded area. Just before the curve a speed hump is in place a short distance from a cross walk. The crosswalk is indicated by green diamond signs on the right hand side of the road.
Figure 3.10.3. Speed Hump Along Horizontal Curve
(Source: Scott Wainwright)

Figure 3.10.4. Speed Hump on a Grade. This figure contains a photograph looking down a hill. The two lane, unmarked road, has an oncoming car in the left lane just about to cross over a speed hump.
Figure 3.10.4. Speed Hump on a Grade
(Source: Scott Wainwright)

EFFECTS AND ISSUES

Effects and Issues – Speed Hump
Vehicle Speed Single speed hump reduces vehicle speeds to the range of 15 to 20 mph when crossing the hump; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed hump; in order to retain slower vehicle speeds over longer distance, series of speed humps is needed (see Figure 3.10.5)

ITE Guidelines for the Design and Application of Speed Humps recommends spacing of 260' to 500' to keep 85th percentile operating speed between 25 and 30 mph; some jurisdictions have refined guidelines:
  • Pennsylvania – spacing between 250 and 600 feet
  • South Carolina – spacing of no less than 350 feet
  • Virginia – spacing of approximately 500 feet, clear visibility of 200 feet, and placement no closer than 200 feet from an intersection
  • Pasadena – speed hump series only on street segment that is at least 1,200 feet in length and traffic signals or Stop signs are at least 1,200 feet apart

Proper placement of initial speed hump in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends that the first speed hump in a series be normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill

Refer to Module 4 for additional data
Vehicle Volume As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed

Refer to Module 4 for additional data
Pedestrian Safety and Mobility Not a preferred location for a crosswalk Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility Bicyclist safety should not be affected; some jurisdictions use maximum street grade of 5 percent on a street with a speed hump if designated as a bicycle route

Bicyclist can negotiate speed hump with little delay or discomfort; it is also possible for a bicyclist to bypass a speed hump by passing through the gap between the hump and the curb and gutter

Refer to Module 6 for additional discussion
Motorist Safety and Mobility Speed effects of a single or series of speed humps are greater than for any other traffic calming measure with the exception of route diversions that eliminate a particular traffic movement

Produces sufficient discomfort to a motorist driving above the speed hump design speed to discourage speeding
Emergency Vehicle Safety and Mobility Typical delay for a fire truck is in the 3 to 5 second range; for an ambulance with a patient, delay can be as much as 10 seconds

Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility Typical delay for a large commercial vehicle is in the 3 to 7 second range

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property Does not typically require removal of any on-street parking or affect accessibility of adjacent property (see Figure 3.10.6)
Environment Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues Placement factors include vertical and horizontal alignment of the street, proximity to the nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.)

Should not require relocation of above- and below-ground utilities

May not be appropriate on a roadway where drainage gutter or flow of water is in the center of the roadway; drainage and hydraulic impacts need careful evaluation

Figure 3.10.5. Series of Speed Humps. This figure contains a photograph of an undivided street in a tree-lined residential area. A sign post with a yellow diamond speed hump sign and a rectangular 15 MPH speed limit sign is on the right hand side of the street. A series of speed humps is visible as the street vanishes into the distance.
Figure 3.10.5. Series of Speed Humps
(Source: City of Stockton, California)

Figure 3.10.6. On-Street Parking Adjacent to Speed Hump. This figure contains a photograph of a curved street in a residential area. A car is parked near the curb beside a signpost with a yellow diamond speed hump sign and a 15 MPH speed limit sign. Other cars can be seen parked on either side of the street.
Figure 3.10.6 Adjacent to Speed Hump
(Source: Lewis Grimm)

ADDITIONAL DESIGN CONSIDERATIONS

ITE provides specific design and application guidance for speed humps; refer to Guidelines for the Design and Application of Speed Humps.

ITE guidelines specify a speed hump that is 12 feet long (in the direction of travel) and 3 inches in height.

A sample design for a speed hump is presented in Figure 3.10.7.

Figure 3.10.7. Sample Design for Speed Hump. This figure contains a line drawing of a speed hump design labeled Delaware Department of Transportation – Typical Speed Hump. The diagram is divided into three parts showing different angles of the sample speed hump, the top/overhead, front-facing, and side cross sections. The overhead portion of the diagram is labeled B to B (horizontal side to side) which includes curbs, and A to A (vertical top to bottom), the dimension in the road in the path of the vehicles. Signing is designated on each side of the lane before the speed hump labeled Speed Hump (W17-1) with a note that reads All signing and striping shall conform to the latest edition of the DE MUTCD. 6-foot wide white angular markings with 12-inch wide stripes are indicated for each side of the speed hump. The diagram also indicates the size of the speed hump, which is variable width and 12 feet for the hump itself in the existing roadway. The central portion of the diagram further elaborates on the design showing a cross-section of B-B (1V=2H) with labels indicating measurements, from left to right: the existing curb, then 1 foot gutter area, and 1 foot 6 inches for a saw cut and 2 foot taper mill rise to a total height of approximately three inches, symmetrical on the other side of the speed hump by the existing curb. The final portion of the diagram shows the A-A (1V=2H) cross section with the 12-foot speed hump in the existing roadway. Starting with a saw cut and 2 foot section with a gradual rise, tapering up to a 3 inch peak, and symmetrically descending to the existing roadway on the opposite side. From the peak, at 1 foot intervals, the height of the speed hump is labeled as 3 inches, 2.9 inches, 2.7 inches, 2.3 inches, 1.7 inches, 0.9 inches.
Figure 3.10.7. Sample Design for Speed Hump
(Source: Delaware Department of Transportation)

3.11 Speed Cushion

DESCRIPTION AND GENERAL PURPOSE

A speed cushion consists of two or more raised areas placed laterally across a roadway (see Figure 3.11.1). The height and length of the raised areas are comparable to the dimensions of a speed hump. The primary difference is that a speed cushion has gaps (often referred to as "cutouts") between the raised areas to enable a vehicle with a wide track (e.g., a large emergency vehicle, some trucks, some buses) to pass though the feature without any vertical deflection.

Another difference between a speed cushion and a speed hump is the common practice for the top of the speed cushion to be level. Like a speed hump, the profile of a speed cushion is gentle enough to provide a comfortable ride when traversed at a speed of approximately 20 to 25 MPH.

[A speed cushion is also known as a speed lump, speed slot, and speed pillow.]

The cutouts in the speed cushions are positioned such that a passenger vehicle cannot pass it without traveling over a portion of the raised pavement.

A speed cushion is often a preferred alternative to a speed hump on a primary emergency response route or on a transit route with frequent service.

[Two field studies of three speed cushions measured reductions between 5 and 7 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_speed.cfm]

Figure 3.11.1. Speed Cushion with Passage that Straddles Centerline. This figure contains a photograph of a tree lined undivided street in a residential area. Three speed cushions are visible, crossing the road from right to left. The right and left cushion are painted with wide white angular stripes indicating a speed cushion. The cushion which straddles the centerline has angular stripes on each side and is narrower than the other two.
Figure 3.11.1. Speed Cushion with Passage that Straddles Centerline
(Source: Jeff Gulden)

APPROPRIATE APPLICATION

Appropriate Application – Speed Cushion
Type of Street Generally appropriate for both local and collector streets
Intersection or Roadway Segment Placed at a midblock location; as an example, Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 feet from a signalized intersection

Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section Can be used on a single-lane one-way or two-lane two-way street (examples are shown in Figures 3.11.2 and 3.11.3)

Typically installed with an urban cross-section (i.e., curb and gutter)12

Can be applied on a cross-section both with and without sidewalks or bicycle facilities
Speed Limit Appropriate maximum speed limit is 30 mph or less (per ITE Guidelines for the Design and Application of Speed Humps); many jurisdictions follow the same maximum speed limit (e.g., South Carolina, Pennsylvania); others have chosen a 25 mph maximum (e.g., Delaware, Pasadena)
Vehicle Traffic Volume Appropriate measure if the daily traffic volume is relatively low; a variety of maximum volumes are in use for speed humps; as examples, Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; on a local level, Pasadena, CA uses a daily volume maximum of 4,000, with at least 1,000 vehicles in each direction

ITE Guidelines for the Design and Application of Speed Humps recommends consideration only if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route Appropriate for a primary emergency vehicle route and on a street that provides access to a hospital or emergency medical services

An emergency vehicle can cross a properly designed speed cushion at a speed near the speed limit
Transit Route Appropriate for a bus transit route
Access Route Appropriate along the primary access to a commercial or industrial site
Grade Can be installed on a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided

IT E Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a grade of 8 percent or less; many jurisdictions adhere to that maximum (e.g. Pennsylvania, South Carolina) but others follow a lower value: Delaware – 6 percent; Minnesota and Pasadena, CA – 5 percent

12 If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the cushion. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

Figure 3.11.2. Speed Cushion with Median. Please see the Extended Text Description below.
Figure 3.11.2. Speed Cushion with Median
(Source: Scott Wainwright)

Figure 3.11.3. Speed Cushion with Continuous Two-Way Left-Turn Lane. This figure contains a photograph of a two-lane street with a continuous two-way left-turn lane in the center running towards an overpass. A speed cushion can be seen crossing the road. A sign post on the right holds a yellow diamond sign which indicates the presence of a speed cushion and a speed limit of 20 MPH.
Figure 3.11.3. Speed Cushion with Continuous Two-Way Left-Turn Lane
(Source: www.pedbikeimages.org / Michael Cynecki)

EFFECTS AND ISSUES

Effects and Issues – Speed Cushion
Vehicle Speed Single speed cushion reduces vehicle speeds to the range of 15 to 20 mph when crossing the cushion; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed cushion; in order to retain slower vehicle speeds over longer distance, a series of speed cushions needed

Average speeds are typically higher than for a speed hump because speed cushion allows a motorist to pass over the cushion with one wheel on the cushion and one wheel off

ITE Guidelines for the Design and Application of Speed Humps recommends spacing of 260' to 500' to keep 85th percentile operating speed between 25 and 30 mph; some jurisdictions have refined guidelines:
  • Pennsylvania – spacing between 250 and 600 feet
  • South Carolina – spacing of no less than 350 feet
  • Virginia – spacing of approximately 500 feet, clear visibility of 200 feet, and placement no closer than 200 feet from an intersection
  • Pasadena – speed cushion series only on street segment that is at least 1,200 feet in length and traffic signals or Stop signs are at least 1,200 feet apart
Proper placement of initial speed cushion in a series is significant; ITE "Guidelines for the Design and Application of Speed Humps" recommends "the first speed [cushion] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill"

Refer to Module 4 for additional data
Vehicle Volume As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed

Refer to Module 4 for additional data
Pedestrian Safety and Mobility Not a preferred location for a crosswalk Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility Bicyclist safety and mobility not affected; bicyclist can pass through the speed cushion gaps

Refer to Module 6 for additional discussion
Motorist Safety and Mobility Speed effects of a single or series of speed cushions are greater than for any other traffic calming measure with the exception of route diversions that eliminate a particular traffic movement

Produces sufficient discomfort to a motorist driving above the speed cushion design speed to discourage speeding

In the UK, where speed cushions are more common than they are currently in the United States, a field study found that 45 percent of passenger car motorists aimed for the gaps when traversing a speed cushion (i.e., one wheel on the hump and one wheel on the flat pavement); this is a safety concern when the speed cushion gaps coincide with the street centerline

A motorcycle can pass through a speed cushion gap without slowing
Emergency Vehicle Safety and Mobility Speed reduction for emergency vehicles is minimal because the larger vehicles can straddle the cushions (see Figure 3.11.4); if the emergency vehicle has the track width of a passenger car (e.g., an ambulance), there is delay

Offset speed table is a comparable vertical measure designed to accommodate emergency vehicle mobility

Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility Speed reduction for large commercial vehicles is minimal because the larger vehicles can straddle the cushions

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property On-street parking does not need to be removed and there is no reduction in accessibility of adjacent property
Environment Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues Placement factors include vertical and horizontal alignment of the street, proximity to the nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.)

Should not require relocation of above- and below-ground utilities

Figure 3.11.4. Fire Truck Approaching Test Speed Cushion. This figure contains a photograph of a residential street with a fire truck approaching a set of test speed cushions with yellow stripes.
Figure 3.11.4. Fire Truck Approaching Test Speed Cushion
(Source: Jeff Gulden)

ADDITIONAL DESIGN CONSIDERATIONS

Pavement markings (e.g., striping, arrows) and signage for a speed cushion should replicate those for a speed hump.

A speed cushion is typically designed with sides that taper off at the gutter for drainage. This design may be modified to end the taper further from the gutter to create a wide, flat surface for a bicycle bypass lane, if desired.

An issue that has generated discussion regarding speed cushion applications is the appropriate cushion width. It is common for heavier vehicles like transit buses and fire trucks to use dual rear wheels. These result in the clear space between the wheels of large vehicles to more closely match the track width of a larger sedan or SUV. The cushion width should be wide enough to slow personal passenger vehicles and yet narrow enough to permit fire trucks and transit vehicles to pass easily, without overloading the rear axles of those heavier vehicles.

Sample designs for speed cushions without and with a median are presented in Figures 3.11.5 and 3.11.6, respectively.

Figure 3.11.5. Sample Design for Speed Cushion without a Median. This figure contains a line drawing of a speed hump design labeled Delaware Department of Transportation – Typical Speed Cushion Detail for a 22" Roadway Section. The diagram is divided into several parts detailing various angles of the design specifications, from overhead view, speed cushion plan view, section A-A (1V=4H) side view, section B-B (1V=4H) side view, with a not-to-scale detail of the tapered side with more specific measurements to the existing roadway. The overhead view details the speed cushion in relation to the existing curb with signage on either side of the road with a note that reads All signing and striping shall conform to the latest edition of the DE MUTCD. The digram shows a road width of 22 feet, with the following components, from top to bottom starting from the existing curb: 2.5 feet maximum spacing from curb, then a 6 foot speed cushion, then 3 feet in between the next speed cushion, then 7 feet for the next speed cushion in the opposite lane, then 2.5 feet maximum spacing from the opposite curb. 12-inch angular markings on each speed cushion are also indicated. The speed cushion plan view further details the design with a 3 foot taper to a flat top on the sides, and 1.5 foot taper to the flat top in the roadway direction. The section A-A view shows a side cross-section of the speed cushion with a saw cut 2 foot taper mill and 1.5 foot rise to the flat top, with a rise to 3 inches at the flat top. Section B-B view shows the roadway cross-section of 12 feet long with a saw cut 2 foot taper mill and 3 foot rise to the flat top of the speed cushion. The 3 foot rise is further detailed with height measurements every 6 inches starting at the peak of 3 inches, then 2.9 inches, 2.6 inches, 2 inches, 1.5 inches and 0.5 inches to the existing roadway.
Figure 3.11.5. Sample Design for Speed Cushion without a Median
(Source: Delaware Department of Transportation)

Figure 3.11.6. Sample Design for Speed Cushion with a Median. This figure contains a line drawing of a speed hump design labeled Delaware Department of Transportation – Typical Speed Cushion Detail for a 32" Roadway Section. The diagram is divided into several parts detailing various angles of the design specifications, from overhead view, speed cushion plan view, section A-A (1V=4H) side view, section B-B (1V=4H) side view, with a not-to-scale detail of the tapered side with more specific measurements to the existing roadway. The overhead view details the speed cushion in relation to the existing curb with signage on either side of the road with a note that reads All signing and striping shall conform to the latest edition of the DE MUTCD. The digram shows a road width of 32 feet, with the following components, from top to bottom starting from the existing curb: 2.5 feet maximum spacing from curb, then a 7 foot speed cushion, then 3 feet in between the next speed cushion, then a 7 foot center speed cushion, which has a center line yellow striping around it, then 7 feet for the next speed cushion in the opposite lane, then 2.5 feet maximum spacing from the opposite curb. 12-inch angular markings on each speed cushion are also indicated. The speed cushion plan view further details the design with a 3 foot taper to a flat top on the sides, and 1.5 foot taper to the flat top in the roadway direction. The section A-A view shows a side cross-section of the speed cushion with a saw cut 2 foot taper mill and 1.5 foot rise to the flat top, with a rise to 3 inches at the flat top. Section B-B view shows the roadway cross-section of 12 feet long with a saw cut 2 foot taper mill and 3 foot rise to the flat top of the speed cushion. The 3 foot rise is further detailed with height measurements every 6 inches starting at the peak of 3 inches, then 2.9 inches, 2.6 inches, 2 inches, 1.5 inches and 0.5 inches to the existing roadway.
Figure 3.11.6. Sample Design for Speed Cushion with a Median
(Source: Delaware Department of Transportation)

3.12 Speed Table

DESCRIPTION AND GENERAL PURPOSE

A speed table is a raised area placed across the roadway designed to physically limit the speed at which a vehicle can traverse it. Like a speed hump, it extends across the travelway. Unlike a speed hump, a speed table has a long enough flat top (typically, 10 feet) to accommodate the entire wheelbase of most passenger cars. The longer longitudinal depth in the direction of travel enables comfortable and safe vehicle operating speeds that are faster than for a speed hump. Figure 3.12.1 illustrates a typical application.

When a speed table is designated as a crosswalk through the use of striping, it is known as a raised crosswalk (see section 3.14).

[Three field studies of 27 speed tables measured crash reductions between 36 and 64 percent (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Crashes, July 2014) http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_crashes.cfm]

[Six field studies of 98 speed tables measured reductions between 4 and 11 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_speed.cfm]

Figure 3.12.1. Typical Speed Table Application. This figure contains an unlined two lane road running through a wooded area. Running across the road is a speed table, a long raised area with a flat top. White angular striping marks the right of way on the speed table. Signposts on both approaches hold a diamond shaped yellow sign that says Speed Table over a rectangular yellow sign that says 15 MPH.
Figure 3.12.1. Typical Speed Table Application
(Source: www.pedbikeimages.org / Austin Brown)

APPROPRIATE APPLICATION

Appropriate Application – Speed Table
Type of Street Can be installed on a local street, collector street, and in certain circumstances, an arterial street
Intersection or Roadway Segment Placed at a midblock location; Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 from a signalized intersection

If placed at an intersection, called a raised crosswalk or raised intersection

Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section Can be used on a single-lane one-way or two-lane two-way street (see Figure 3.12.2)

Typically installed with an urban cross-section (i.e., curb and gutter)13 but an open section can be acceptable

Can be applied both with and without sidewalks or bicycle facilities
Speed Limit ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a posted speed limit of 30 mph or less; many jurisdictions follow the same maximum (e.g., South Carolina, Pennsylvania); others have chosen a 35 mph maximum (e.g., Delaware, Pasadena)

Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume Some jurisdictions provide guidance on a maximum traffic volume that can be properly accommodated; Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; Pasadena, CA uses a maximum of 4,000, with at least 1,000 vehicles in each direction

ITE Guidelines for the Design and Application of Speed Humps recommends consideration if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route Generally not appropriate for a primary emergency vehicle route or street that provides access to a hospital or emergency medical services; another form of vertical deflection – a speed cushion -could be appropriate
Transit Route Generally not appropriate for a bus transit route with BRT, Express, or Limited Stop service (unless the posted speed limit is 30 mph or less); speed cushion could be appropriate

Can be appropriate along a neighborhood circulator or other local bus service route

Should not be located near bus stop to insure passengers are not transitioning between standing and sitting as the bus crosses over the speed table
Access Route Not appropriate along the primary access to a commercial or industrial site
Grade Can be installed on, or beyond, a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided

ITE Guidelines for the Design and Application of Speed Humps recommends consideration only with a grade of 8 percent or less; many jurisdictions adhere to that maximum grade (e.g. Pennsylvania, South Carolina) but others follow a lower maximum: Delaware – 6 percent; Minnesota – 5 percent

13 If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the table. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

Figure 3.12.2. Speed Table with Choker. This figure contains a photograph of a residential area. On the left hand side of the photo there is a lane of trees on a landscaped median. To the right of the trees there is single lane road labeled Harn Blvd. A speed table, dyed a dusty pink, fills most of the lane. This traffic feature also uses a choker, a crescent shaped curb extension landscaped with shrubs that extends onto the speed table. To the right of that, there is a sidewalk separating the street from a row of single story houses.
Figure 3.12.2. Speed Table with Choker
(Source: Google Street View)

EFFECTS AND ISSUES

Effects and Issues – Speed Table
Vehicle Speed Single speed table reduces 85th percentile speeds to the range of 25 to 35 mph when crossing the table; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed table; in order to retain slower vehicle speeds over a longer distance, a series of speed tables is needed (as shown in Figure 3.12.3)

ITE Guidelines for the Design and Application of Speed Humps recommends a spacing of between 260 and 500 feet; some jurisdictions have refined these guidelines:
  • Pennsylvania – spacing between 250 and 600 feet
  • South Carolina – spacing of no less than 350 feet
  • Virginia – spacing of approximately 500 feet, with clear visibility of 200 feet, and placement no closer than 200 feet from an intersection
  • Pasadena – only on a street segment that is at least 1,200 feet in length and on which any traffic signals or Stop signs are at least 1,200 feet apart
Proper placement of the initial speed table in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends "the first speed [table] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill"

Refer to Module 4 for additional data
Vehicle Volume As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed

Refer to Module 4 for additional data
Pedestrian Safety and Mobility Appropriate location for a crosswalk; in traffic calming terms, a crosswalk on a speed table is called a raised crosswalk [provide link to section 3.14]

Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility Bicyclist safety should not be affected; some jurisdictions use a maximum street grade of 5 percent if the street is designated as a bicycle route

Bicyclist can negotiate a speed table with little delay or discomfort; it is also possible to bypass speed table by passing through the gap between the table and the curb and gutter
Motorist Safety and Mobility Produces sufficient discomfort to a motorist driving above the speed table design speed to discourage speeding

Can be constructed with brick or other textured materials on the flat section
Emergency Vehicle Safety and Mobility Less speed delay than for a speed hump

Has less jarring effect on long, stiff-bodied emergency service vehicle than speed hump

Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility Larger vehicle typically crosses at slower speed than does a personal passenger motor vehicle

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property May result in the removal of on-street parking adjacent to speed table, on both sides of the street

Should be placed at least five feet from a driveway for comfort
Environment Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues Placement factors include vertical and horizontal alignment of street, proximity to nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.)

Should not be located as to require the relocation of above-ground and below-ground utilities

A speed table does not extend from curb to curb

Typically, does not interfere with drainage because table does not extend from curb to curb; however, if drainage gutter or flow of water is in the center of the roadway, drainage and hydraulic impacts need to be evaluated

Figure 3.12.3. Speed Table in a Series. This figure contains a photograph of a two lane road divided by double yellow lines curving from the bottom left of the picture to near its right edge and back to the center. A speed table is visible before the curve begins, striping painted on it to indicate right of way. On either side of the road, there is a signpost holding a diamond shaped yellow sign which says Speed Table. To the left of the road there is a hill with scrub brush. An additional speed table can be seen after the curve. The shoulder off of the right side is dirt and gravel
Figure 3.12.3. Speed Table in a Series
(Source: James R. Barrera)

ADDITIONAL DESIGN CONSIDERATIONS

Most agencies implement speed tables with a height of between 3 and 3.5 inches and an overall travel length of 22 feet. The most common speed table consists of a 10 foot plateau with 6 foot approaches on both sides that can be straight, parabolic or sinusoidal in profile. Speed tables with heights as great as 6 inches, ramps of up to 10 feet, and plateaus between 18 and 23 feet in length have been tested and found to better accommodate large vehicles with long wheelbases (such as fire trucks and transit buses).

A speed table should be clearly marked, so all roadway users are able to anticipate it and reduce their speeds appropriately.

[The primary difference between a speed table design and a raised crosswalk design is the height and manner in which it meets the curb: with or without a side taper.]

3.13 Offset Speed Table

DESCRIPTION AND GENERAL PURPOSE

An offset speed table is a raised area placed across the roadway designed to physically limit the speed at which a vehicle can traverse it. Like a speed table, it extends across the travelway and has a long enough flat top (typically, 10 feet) to accommodate the entire wheelbase of most passenger cars.

The offset speed table is split down the centerline of the street with the two halves separated longitudinally (as shown in Figure 3.13.1). The offset tables enable an emergency response vehicle to bypass the speed tables by travelling in the opposing traffic lane for a short distance. This maneuver removes most of the emergency vehicle delay associated with a standard speed table.

Figure 3.13.1. Offset Speed Table. This figure contains a photograph of a straight two lane road divided by a double yellow line. In the near distance in the right lane only, there is a speed table with striping indicating the right of way. A car length further away, there is an offset speed table in the left hand lane. Raised reflectors separate the lanes in between the two speed tables. Off of the left hand side of the street there are apartments in the distance.
Figure 3.13.1. Offset Speed Table
(Source: Jeff Gulden)

APPROPRIATE APPLICATION

Appropriate Application – Offset Speed Table
Type of Street Can be installed on a local street, collector street, and in certain circumstances, an arterial street
Intersection or Roadway Segment Placed at a midblock location; Pennsylvania recommends a distance of 150 feet from an unsignalized intersection and 250 feet from a signalized intersection

Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section Appropriate for a two-lane two-way street

Typically installed with an urban cross-section (i.e., curb and gutter)14 but an open section can be acceptable

Can be applied both with and without sidewalks or bicycle facilities
Speed Limit ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a posted speed limit of 30 mph or less; many jurisdictions follow the same maximum (e.g., South Carolina, Pennsylvania); others have chosen a 35 mph maximum (e.g., Delaware, Pasadena)

Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume Some jurisdictions provide guidance on a maximum traffic volume that can be properly accommodated; Pennsylvania sets a maximum daily volume of 3,500; South Carolina uses a maximum of 4,000; Pasadena, CA uses a maximum of 4,000, with at least 1,000 vehicles in each direction

ITE Guidelines for the Design and Application of Speed Humps recommends consideration if no more than five percent of the overall traffic flow consists of long-wheelbase vehicles
Emergency Route Can be appropriate for a primary emergency vehicle route or street that provides access to a hospital or emergency medical services; another form of vertical deflection – a speed cushion – could also be appropriate
Transit Route Generally not appropriate for a bus transit route with BRT, Express, or Limited Stop service (unless the posted speed limit is 30 mph or less); speed cushion could be appropriate

Can be appropriate along a neighborhood circulator or other local bus service route

Should not be located near bus stop to ensure passengers are not transitioning between standing and sitting as the bus crosses over the offset speed table
Access Route Not appropriate along the primary access to a commercial or industrial site
Grade Can be installed on, or beyond, a crest vertical curve only if there is adequate stopping sight distance or warning signs are provided

ITE Guidelines for the Design and Application of Speed Humps recommends consideration only with a grade of 8 percent or less; many jurisdictions adhere to that maximum grade (e.g. Pennsylvania, South Carolina) but others follow a lower maximum: Delaware – 6 percent; Minnesota – 5 percent

14 If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the table. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

EFFECTS AND ISSUES

Effects and Issues – Offset Speed Table
Vehicle Speed Single offset speed table reduces 85th percentile speeds to the range of 20 to 30 mph when crossing the table; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a speed table; in order to retain slower vehicle speeds over a longer distance, a series of speed tables is needed

ITE Guidelines for the Design and Application of Speed Humps recommends a spacing of between 260 and 500 feet; some jurisdictions have refined these guidelines:
  • Pennsylvania – spacing between 250 and 600 feet
  • South Carolina – spacing of no less than 350 feet
  • Virginia – spacing of approximately 500 feet, with clear visibility of 200 feet, and placement no closer than 200 feet from an intersection
  • Pasadena – only on a street segment that is at least 1,200 feet in length and on which any traffic signals or Stop signs are at least 1,200 feet apart
Proper placement of the initial speed table in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends "the first speed [table] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill"

Refer to Module 4 for additional data
Vehicle Volume As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed

Refer to Module 4 for additional data
Pedestrian Safety and Mobility Not a preferred location for a crosswalk
Bicyclist Safety and Mobility Bicyclist safety should not be affected; some jurisdictions use a maximum street grade of 5 percent if the street is designated as a bicycle route

Bicyclist can negotiate a speed table with little delay or discomfort; it is also possible to bypass speed table by passing through the gap between the table and the curb and gutter
Motorist Safety and Mobility Produces sufficient discomfort to a motorist driving above the speed table design speed to discourage speeding

Can be constructed with brick or other textured materials on the flat section
Emergency Vehicle Safety and Mobility Minimal delay for emergency service vehicle that bypasses tables Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility Larger vehicle typically crosses at slower speed than does a personal passenger motor vehicle

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property May result in the removal of on-street parking adjacent to offset speed table, on both sides of the street

Should be placed at least five feet from a driveway for comfort
Environment Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues Placement factors include vertical and horizontal alignment of street, proximity to nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.)

Driver circumnavigation can be minimized with small median islands leading up to each table, with double-centerline and raised pavement markers

Should not be located as to require the relocation of above-ground and below-ground utilities

Typically, does not interfere with drainage; but roadway, drainage and hydraulic impacts should be evaluated

ADDITIONAL DESIGN CONSIDERATIONS

The spacing between offset speed tables is typically a minimum of 50 feet (measured between the closest taper edges).

Typical height of offset speed tables is between 3 and 3.5 inches, with an overall travel length of 22 feet. The most common speed table consists of a 10 foot plateau with 6 foot approaches on both sides that can be straight, parabolic or sinusoidal in profile. Speed tables with heights as great as 6 inches, ramps of up to 10 feet, and plateaus between 18 and 23 feet in length have been tested and found to better accommodate large vehicles with long wheelbases (such as fire trucks and transit buses).

An offset speed table should be clearly marked, so all roadway users are able to anticipate it and reduce their speeds appropriately.

3.14 Raised Crosswalk

DESCRIPTION AND GENERAL PURPOSE

A raised crosswalk is a variation of a flat-topped speed table. A raised crosswalk is marked and signed as a pedestrian crossing. The 10-foot flat top on a typical speed table conforms to a desired crosswalk width (see Figure 3.14.1).

There are two distinct raised crosswalk designs. Both use a modified version of the common 22-foot speed table:

A raised crosswalk improves pedestrian safety by causing motorist speed to decrease at the crossing (see Figure 3.14.2).

A raised crosswalk is typically between 3 and 6 inches above street level. It is common for a raised crosswalk to be level with the street curb. This height increases the visibility of a pedestrian in a crosswalk to a motorist. It also improves the line of sight for a pedestrian toward an oncoming vehicle.

A raised crosswalk can be placed midblock or at an intersection.

A stop-animation film that demonstrates the benefits of a raised crosswalk can be accessed at the following hyperlink: http://www.streetfilms.org/raised-crosswalk/ (Source: Streetfilms)

A video of pedestrians, bicyclists, and motor vehicles passing over a raised crosswalk can be accessed at the following hyperlink:

http://www.yargerengineering.com/articles/traffic calming.html#Raised crosswalk (Source: Yarger Engineering, Inc.)

Figure 3.14.1. Raised Crosswalk Schematic. This figure contains a line drawing of an overhead view showing a two lane road. Three evenly spaced houses are on either side. Icons representing trees are scattered near sidewalks. A raised crosswalk is represented crossing the road approximately four car lengths from the left hand side of the drawing. A car is about to cross it in the bottommost lane. Another vehicle approaches the crosswalk in the topmost lane. A vehicle is parked in the driveway of the center house above the topmost lane.
Figure 3.14.1. Raised Crosswalk Schematic
(Source: Delaware Department of Transportation)

Figure 3.14.2. Typical Raised Crosswalk Application. This figure contains a photograph of a two lane street in a business district. A sidewalk on the right hand side of the picture has a signpost holding a diamond shaped yellow sign showing an icon of a person walking over the words Raised Crosswalk. Between the curb and the right lane there is parallel parking where a red truck and another vehicle are parked. A light colored car and another truck have just crossed the walk in the right hand lane. The left lane is free of traffic. A raised crosswalk connects the sidewalks on the sides of the street.
Figure 3.14.2. Typical Raised Crosswalk Application
(Source: Jeff Gulden)

APPROPRIATE APPLICATION

Appropriate Application – Raised Crosswalk
Type of Street Appropriate if there is an existing crosswalk in the approximate crossing location or if a crosswalk is warranted based on local standards and criteria

Generally installed on a residential local street or a collector street (or on a low-speed arterial street through a commercial district)
Intersection or Roadway Segment Can be placed at a midblock location (see Figure 3.14.3) or at an intersection (see Figure 3.14.4)

Should not be placed on a sharp curve; ITE Guidelines for the Design and Application of Speed Humps recommends a minimum horizontal curve radius of 300 feet
Roadway Cross-Section Can be used on a single-lane one-way or two-lane two-way street

Typically installed with an urban cross-section (i.e., curb and gutter)15 but an open section can be acceptable

Cross-section can include on-street parking

Can be applied both with and without sidewalks or bicycle facilities
Speed Limit ITE Guidelines for the Design and Application of Speed Humps recommends consideration only on a street with a posted speed limit of 30 mph or less; many jurisdictions follow the same maximum (e.g., South Carolina, Pennsylvania); others have chosen a 35 mph maximum (e.g., Delaware, Pasadena)

Generally not appropriate when the pre-implementation 85th percentile speed is 45 mph or more
Vehicle Traffic Volume A maximum traffic volume could be appropriate if the raised crosswalk functions more as a speed table; however, many raised crosswalks are installed at locations with high pedestrian volume, high vehicle volume, and low vehicle speed (for example, in a downtown)
Emergency Route Generally not appropriate for a primary emergency vehicle route or street that provides access to a hospital or emergency medical services
Transit Route Can be appropriate for a bus transit route if typical bus operating speeds are in 25 mph range

Should not be located near bus stop to insure passengers are not transitioning between standing and sitting as the bus crosses over raised crosswalk
Access Route Not appropriate along the primary access to a commercial or industrial site
Grade Can be installed on a crest vertical curve only if there is adequate stopping sight distance or appropriate warning signs provided

ITE Guidelines for the Design and Application of Speed Humps recommends consideration only with a grade of 8 percent or less; many jurisdictions adhere to that maximum grade (e.g. Pennsylvania, South Carolina; Portland OR) but others follow a lower maximum: Delaware – 6 percent; Minnesota – 5 percent

15 If the street does not have curbing, an obstruction such as signing, flexible delineator posts, or bollards may be acceptable to prevent a motorist from driving around the table. Potentially hazardous objects (e.g., rocks, boulders) should not be used.

Figure 3.14.3. Raised Crosswalk Midblock. This figure contains a photograph of a raised crosswalk on a slightly curved two lane road divided by dashed lines. A sidewalk follows the road on its right side. A signpost holding a diamond shaped yellow sign with icon of a person walking and a fluorescent green rectangular sign with a black arrow pointing downwards at a slight angle is to the right of the sidewalk. The raised crosswalk, with painted arrows indicating right of way and a white ladder shape indicating where to cross, connects the sidewalk and a full parking lot. A sidewalk curves away from the left hand side of the crosswalk and down. Fencing and a strand of thin trees separate the parking lot from the road.
Figure 3.14.3. Raised Crosswalk Midblock
(Source: R. Goldberg)

Figure 3.14.4. Raised Crosswalk at Intersection. This figure contains a photograph of a raised crosswalk at an intersection taken from the point of view of a pedestrian. The white striped pattern crosses to a sidewalk which stretches up the center of the photo. To the right of the sidewalk, there is a red brick single story building. A signpost to the right of the crosswalk just at the curb holds a Do Not Enter sign and a One Way sign pointing to the left. Across the sidewalk from that there is a red fire hydrant and a crosswalk sign. Trees and business line the street to the left of the sidewalk.
Figure 3.14.4. Raised Crosswalk at Intersection
(Source: City of Cambridge, Massachusetts)

EFFECTS AND ISSUES

Effects and Issues – Raised Crosswalk
Vehicle Speed Single raised crosswalk reduces 85th percentile speeds to the range of 20 to 30 mph when crossing the crosswalk; speed reduction effects decline at the rate of approximately 0.5 to 1 mph every 100 feet beyond the 200 foot approach and exit of a raised crosswalk; in order to retain slower vehicle speeds over a longer distance, a series of speed tables or raised crosswalks is needed

ITE Guidelines for the Design and Application of Speed Humps recommends a spacing of between 260 and 500 feet; some jurisdictions have refined these guidelines:
  • Pennsylvania – spacing between 250 and 600 feet
  • South Carolina – spacing of no less than 350 feet
  • Virginia – spacing of approximately 500 feet, with clear visibility of 200 feet, and placement no closer than 200 feet from an intersection
  • Pasadena – only on a street segment that is at least 1,200 feet in length and on which any traffic signals or Stop signs are at least 1,200 feet apart
Proper placement of the initial raised crosswalk in a series is significant; ITE Guidelines for the Design and Application of Speed Humps recommends "the first [raised crosswalk] in a series is normally located in a position where it cannot be approached at high speed from either direction; to achieve this objective, it is typically installed within 200 feet or less of a small-radius curve or Stop sign or, if installed on a street with a significant downgrade, at the top of a hill"

Refer to Module 4 for additional data
Vehicle Volume As single installation, there is little traffic diversion from the street; as part of a series, typical volume reductions of 20 percent observed

Refer to Module 4 for additional data
Pedestrian Safety and Mobility Pedestrian safety improved because (1) vehicle speed is lowered at crosswalk, (2) pedestrian in a raised crosswalk is more visible to an oncoming motorist and (3) pedestrian has an elevated view of oncoming traffic; raised crosswalk could be combined with a curb extension to provide additional visibility for pedestrian (see Figure 3.14.5)

If raised crosswalk is the same height as the curb, edge of the raised crosswalk should be differentiated with a detectable warning or truncated domes to warn a person with a visual impairment

Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility Bicyclist safety should not be affected; some jurisdictions use a maximum street grade of 5 percent if the street is designated as a bicycle route

Bicyclist can negotiate a raised crosswalk with little delay or discomfort (see Figure 3.14.6)
Motorist Safety and Mobility Produces sufficient discomfort to a motorist driving above the raised crosswalk design speed to discourage speeding
Emergency Vehicle Safety and Mobility Less speed delay than for a speed hump

Has less jarring effect on long, stiff- bodied emergency service vehicle

Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility Larger vehicle typically crosses at slower speed than does a personal passenger motor vehicle

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property May result in the removal of on-street parking adjacent to raised crosswalk, on both sides of the street

Typically placed at least five feet from a driveway but can be designed to incorporate a driveway
Environment Potential for increased noise due to vehicle braking and accelerating and to the vibration of loose items in truck beds or trailers
Design Issues Placement factors include vertical and horizontal alignment of street, proximity to nearest intersection, location of driveways and on-street parking, presence or absence of street lighting, location of designated pedestrian crossings, drainage, and utility access points (drains, valves, etc.)

Extends from curb to curb and therefore affects surface drainage on the roadway; likely that a catch basin will be required on the upstream side of the raised crosswalk; drainage and hydraulic impacts need to be evaluated

Should not be located as to require the relocation of above-ground and below-ground utilities

Figure 3.14.5. Raised Crosswalk with Curb Extension. This figure contains a photograph of a tree-lined residential area. The focus is a road which runs from the bottom middle of the photo up to the top middle. The road narrows at approximately the halfway point using a curb extension. There is a raised crosswalk that leads from the curb extension to the opposite corner of a sidewalk. Just above the crosswalk, there is an intersection.
Figure 3.14.5. Raised Crosswalk with Curb Extension
(Source: Scott Batson)

Figure 3.14.6. Raised Crosswalk with Bicycle Lane. his figure contains a photograph of a city street which runs diagonally from bottom left to top right of the photo. To the right of the right lane, there is a bicycle lane marked with solid white lines and space for parallel parking near the curb. To the right of the crosswalk there is a phone pole holding a diamond sign with the icon of a person walking and a bicycle. There is a rectangular sign below that with an arrow pointing slightly down and to the left. Below that there is a green rectangular sign with a bicycle on it. Across the raised crosswalk, there are trees and a row of houses and other buildings.
Figure 3.14.6. Raised Crosswalk with Bicycle Lane
(Source: Scott Batson)

ADDITIONAL DESIGN CONSIDERATIONS

The primary difference between a speed table design and a raised crosswalk design is the height and manner in which it meets the curb.

Most agencies implement raised crosswalks with a height of between 3 and 3.5 inches and an overall travel length of 22 feet. The most common raised crosswalk consists of a 10 foot plateau with 6 foot approaches on either side that can be straight, parabolic, or sinusoidal in profile.

A raised crosswalk requires incorporation of all the standard crosswalk design elements. The markings must be visible to motorists, especially at night.

For a raised crosswalk, the longitudinal drainage taper can be removed to form a level pedestrian crossing. Drainage will still need to be provided, such as by using a trench drain through the raised crosswalk and covered with an ADA-compliant grate (see Figure 3.14.7). Another option is to place the drainage inlet upstream of the raised crosswalk.

A raised crosswalk should be clearly marked, so all roadway users are able to anticipate it and reduce their speeds appropriately.

So that a person with visual impairment can differentiate the roadway from the sidewalk at a raised crosswalk, color contrasts and detectable warnings or truncated domes at edges can enable a pedestrian with a vision impairment to detect the crossing.

A sample design for a raised crosswalk is presented in Figure 3.14.8.

Figure 3.14.7. Raised Crosswalk Design to Accommodate Drainage. This figure contains a photograph of a street from the bottom left to the top right of the photo. The raised crosswalk has pale concrete ramps and a red brick crosswalk. A gutter allows drainage on the right hand side of the crosswalk and a metal plate covers it to allow foot traffic to easily use the crosswalk. A signpost between the crosswalk and sidewalk holds a yellow diamond sign which says Raised Crosswalk and a white rectangular sign which says Begin One Way. A sidewalk runs beside the road separated from it by a row of trees. A van is crossing the walk and across the street there is a large red brick apartment building. Space for parallel parking is available on either side of the street
Figure 3.14.7. Raised Crosswalk Design to Accommodate Drainage
(Source: Jeff Gulden)

Figure 3.14.8. Sample Design for Raised Crosswalk. This figure contains a line drawing of a raised crosswalk design labeled Delaware Department of Transportation – Typical Raised Crosswalk. The diagram is divided into three parts showing different angles of the sample raised crosswalk, the top/overhead, front-facing, and side cross sections. The overhead portion of the diagram is labeled B to B (horizontal side to side), and A to A (vertical top to bottom), the dimension in the roadway in the path of the vehicles. The diagram also indicates the size of the raised crosswalk, with a variable width, but 22 feet in the roadway itself, with an ADA pedestrian ramp connecting the sidewalk to the crosswalk and existing curb, with standard crosswalk pavement markings per DE MUTCD. The central portion of the diagram further elaborates on the design showing a cross-section of A-A (1V=2H) with labels indicating measurements, from left to right: the existing roadway, then 2 feet for initial rise then a parabolic rise over 6 feet to a 10 foot flat surface, then a graduated symmetrical descent on the other side to the roadway area, marked in 1 foot divisions with the following heights from a 3 inch peak: 3 inches, 2.9 inches, 2.7 inches, 2.3 inches, 1.7 inches, 0.9 inches to the existing roadway. The final portion of the diagram shows the B-B (1V=2H) cross section showing from left to right, the existing roadway, variable width but a height of 3 inches, then the depressed curb and an ADA pedestrian ramp of variable width. Notes at the bottom read 1. Inlets are required on the uphill side of a raised crosswalk and 2. All signing and striping shall conform to the latest edition of the DE MUTCD.
Figure 3.14.8. Sample Design for Raised Crosswalk
(Source: Delaware Department of Transportation)

3.15 Raised Intersection

DESCRIPTION AND GENERAL PURPOSE

A raised intersection is a flat, raised area covering an entire intersection with ramps on all approaches. It is essentially a speed table that covers an entire intersection, including the crosswalks (see Figure 3.15.1).

The purpose of a raised intersection is to slow vehicle traffic through the intersection and to improve safety for pedestrians. It has the advantage of calming two streets at once.

A raised intersection typically rises to sidewalk level.

A raised intersection is especially applicable in a dense urban area (see Figure 3.15.2). A typical installation is at a signal-controlled or all-way stop-controlled intersection with a large volume of street-crossing pedestrians. A raised intersection reinforces the need for a motorist to drive cautiously and be wary of crossing pedestrians.

[A raised intersection is also called a raised junction, intersection hump, or plateau.]

[Two field studies of five raised intersections measured reductions between 1 and 5 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_speed.cfm]

A video of pedestrians, bicyclists, and motor vehicles passing over a raised intersection can be accessed at the following hyperlink:

http://www.yargerengineering.com/articles/traffic calming.html#Raised intersections (Source: Yarger Engineering, Inc.)

Figure 3.15.1. Raised Intersection. This figure contains a photograph of a commercial area including a two lane street running from bottom left to upper right of the photo. The raised intersection, a speed table covering the entire intersection, dominates the center of the photo. The ramps are darker and the plateau is a light red. To the right of the raised intersection there is a sidewalk and a concrete flower box filled with a dark red and green plant. To the left of the intersection there are a row of shops. One car is moving through the intersection and there are cars parked in parallel behind it.
Figure 3.15.1. Raised Intersection
(Source: Yarger Engineering, Inc.)

Figure 3.15.2. Raised Intersection in Dense Urban Setting. This figure contains a picture of a two lane, one way road between two strands of palm trees and multi-story buildings. There is oncoming traffic in both lanes. Two entrances to the raised intersection can be seen. The intersection itself is done in light red brick.
Figure 3.15.2. Raised Intersection in Dense Urban Setting
(Source: Ian Lockwood)

APPROPRIATE APPLICATION

Appropriate Application – Raised Intersection
Type of Street Appropriate if there are existing crosswalks on all four legs of the intersection or if crosswalks are warranted

Appropriate for the intersection of collector, local, and residential subdivision streets

Can be appropriate in both a residential setting (see Figure 3.15.3) and in a commercial business district

Could be acceptable on a low-speed arterial in a downtown business district with significant pedestrian activity
Intersection or Roadway Segment Placed at an intersection

Can be a T-intersection or multi-leg intersection
Roadway Cross-Section Approach legs can be either one-way or two-way

Appropriate only with an urban cross-section (i.e., curb and gutter) that includes sidewalks on all sides of the intersection

Can include on-site parking on the approach legs

Appropriate if a bicycle facility passes through the intersection
Speed Limit Maximum speed limit of 30 mph based on ITE Guidelines for the Design and Application of Speed Humps and some jurisdictions (e.g., South Carolina, Pennsylvania); others use a 35 mph maximum (e.g., Delaware)
Vehicle Traffic Volume Appropriate if the daily traffic volume on each intersection approach is relatively low; example thresholds include Pennsylvania with a maximum of 10,000 vehicles per day and South Carolina which uses 4,000 on each leg in a residential setting and 6,000 on each leg in a commercial area
Emergency Route Can be an appropriate application for a primary emergency vehicle route or on street that provides access to a hospital or emergency medical services
Transit Route Can be an appropriate application for a bus transit route
Access Route Generally not appropriate along the primary access to a commercial or industrial site
Grade Can be installed on a crest vertical curve only if there is adequate stopping sight distance or if appropriate warning signs are provided

Maximum grade of 8 percent recommended in ITE Guidelines for the Design and Application of Speed Humps and used by some jurisdictions (e.g., Pennsylvania, South Carolina); Delaware uses a maximum of 6 percent; Minnesota uses a maximum of 5 percent

Figure 3.15.3. Raised Intersection in Residential Setting without Raised Crosswalks. This figure contains a photograph of undivided two lane roads intersecting at the center of the photo. The road running from top to bottom, Franklin St., features parallel parking on the right hand side and a car approaches the intersection. There is a signpost to the right of Franklin, at the intersection, with a yellow diamond sign with the words Speed Hump and a square yellow sign below that which contains the text 15 MPH. There are houses on the opposite side of the intersection. Arrows painted between the crosswalks and the raised pavement indicate right of way. The raised intersection is bordered in white stripes and sidewalks.
Figure 3.15.3. Raised Intersection in Residential Setting without Raised Crosswalks
(Source: Google Street View)

EFFECTS AND ISSUES

Effects and Issues – Raised Intersection
Vehicle Speed A single raised intersection reduces 85th percentile speeds to the range of 25 to 35 mph when crossing the intersection; vehicle speeds at some distance from the intersection have not been shown to change appreciably
Vehicle Volume As a single installation, there is little traffic diversion from the intersection
Pedestrian Safety and Mobility Pedestrian safety is improved because a pedestrian is more visible to an oncoming motorist and the pedestrian has an elevated view of oncoming traffic (see Figure 3.15.4)

If the same height as the curb, the edge of the raised intersection should be differentiated with a tactile measure to warn a person with a visual impairment

Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility Should not be affected by a raised intersection unless pavers (or some other textured surface) are used
Motorist Safety and Mobility Produces sufficient discomfort to a motorist driving above the raised intersection design speed to discourage speeding
Emergency Vehicle Safety and Mobility A large emergency vehicle typically crosses a raised intersection at a slower speed than does a personal passenger motor vehicle

Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility A larger vehicle typically crosses a raised intersection at a slower speed than does a personal passenger motor vehicle; a typical raised intersection delay for a large commercial vehicle is in the range of 2 to 6 seconds

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property Should not result in any change in accessibility to property along all legs of the intersection; on-street parking restrictions and driveway accessibility should be the same whether intersection is raised or level
Environment Can serve as a form of gateway treatment at or near the entrance to an area for which traffic calming is desired

Traffic noise may increase from braking and acceleration of vehicles
Design Issues Likely requires changes in access to below-ground utilities

Requires redesign of surface drainage structures that serve the intersection and approach legs

Figure 3.15.4. Raised Intersection with Raised Crosswalks. This figure contains a photograph dominated by a closeup of a raised intersection with raised crosswalks. The crosswalks are indicated by thick white stripes. The raised intersection is made of light red bricks. Two story houses occupy the far corners. There is parallel parking space on either side of the two lane street divided by double yellow lines. An oncoming car can be seen approaching the raised intersection.
Figure 3.15.4. Raised Intersection with Raised Crosswalks
(Source: Google Street View)

ADDITIONAL DESIGN CONSIDERATIONS

The design of a raised intersection needs to pay close attention to the existing drainage systems because the grade of the entire intersection will be raised. Additional (or relocated) drainage inlets will likely be required.

In order to enable a pedestrian with a visual impairment to differentiate between the roadway and the sidewalk, measures such as color contrasts and detectable warning truncated domes at edges must be included.

A minimum pavement slope of 1 percent (or the local practice standard) should be provided within the raised intersection to facilitate surface drainage. Surface drainage implications on the approaches to a raised intersection should also be addressed.

A sample design for a raised intersection is presented in Figure 3.15.5.

Figure 3.15.5. Sample Design for Raised Intersection. This figure contains a line drawing of a design for a typical raised intersection. The drawing is labeled Delaware Department of Transportation – Typical Raised Intersection. The drawing shows two lane streets divided by solid double lines. Sidewalks line the streets, curving at each angle of the intersection. The section of road to the right of the intersection is labeled with a double arrow showing the typical width of the road to be twenty four feet. The intersection has an appearance of being made of brick and is labeled Optional Patterned Pavement. The rise is hatched with diagonal lines. Below the top portion of the diagram is a side view cross section showing the parabolic rise of the intersection, labeled Section A-A. The rise from the existing roadway is indicated as 6 feet in length, labeled at 1 foot increments with the following parabolic rise: 3 feet, 2.9 feet, 2.7 feet, 2.3 feet, 1.7 feet, 0.9 feet, down to the existing roadway. A note at the bottom indicates that all signing and striping shall conform to the latest edition of the DE MUTCD.
Figure 3.15.5. Sample Design for Raised Intersection
(Source: Delaware Department of Transportation)

3.16 Corner Extension/Bulbout

DESCRIPTION AND GENERAL PURPOSE

[Other terms include neckdown, corner extension, pop-out, bump out, knuckle and nub. If coupled with a crosswalk, a roadway narrowing can be referred to as a safe cross. When placed at the entrance to a neighborhood, often with textured paving between a pair of them, a bulb-out or corner extension is called a gateway or entry feature.]

A curb extension is a horizontal extension of the sidewalk into the street resulting in a narrower roadway section (see Figure 3.16.1). This device may be used at either corner or midblock. A curb extension at an intersection is called a corner extension or bulbout. A curb extension located midblock is called a choker [provide link to section 3.17].

When combined with on-street parking, a corner extension can create a protected parking bay.

The effect of a corner extension on vehicle speeds is limited because of the absence of either a pronounced vertical or horizontal deflection. Its primary purpose is to "pedestrianize" an intersection. A corner extension (with a reduced corner radius) slows automobile turning speeds, shortens pedestrian crossing distance, and increases pedestrian visibility (see Figure 3.16.2).

When a corner extension is part of a downtown redevelopment project, it can go hand-in-hand with on-street parking bays and crosswalks (in "safe cross" designs).

A corner extension can be combined with a vertical speed control device (e.g., a raised crosswalk) to achieve a greater reduction in vehicle speed.

[Two field studies of five corner extensions measured reductions between 1 and 3.5 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_speed.cfm]

Figure 3.16.1. Corner Extension Schematic. This figure contains a line drawing of the use of corner extensions in an intersection. The top left and right and bottom right corners contain houses. The street running left to right is narrowed at the intersection by rounded corner extensions jutting out into the street. There is a truck in the bottom lane of the left hand street. A van waits in the left hand lane of the top section of street. A car has passed through the intersection and is in the left hand lane in the bottom section of street.
Figure 3.16.1. Corner Extension Schematic
(Source: Delaware Department of Transportation)

Figure 3.16.2. Corner Extension with Shortened Pedestrian Crossing Distance. This figure contains a photograph of an intersection. The focus is on a section of street running from the bottom right hand corner of the picture to the top left hand corner of the picture. The crosswalk nearest the bottom of the picture has a pedestrian crossing the shortened section with a corner extension. A bike lane double arrow is painted on the street nearest the bottom edge of the picture, the arrows pointing down. The road on the far side of the intersection is two lane divided by a double yellow line. Trees line the left hand side of the street. Houses and trees line the street on the right hand side.
Figure 3.16.2. Corner Extension with Shortened Pedestrian Crossing Distance
(Source: Hillary Orr)

APPROPRIATE APPLICATION

Appropriate Application – Corner Extension/Bulbout
Type of Street Appropriate for all street classifications – arterial, collector, or local street

Can be appropriate in both an urban and suburban setting (see Figures 3.16.3 and 3.16.4)
Intersection or Roadway Segment Applicable only at an intersection; if placed midblock, considered a choker [provide link to section 3.17]

Can be applied on any or all of the approach legs of an intersection with any number of legs
Roadway Cross-Section Can be used on both one-way and two-way streets

Can be installed only on a roadway with an urban cross-section (i.e., curb and gutter)

Can be applied both with and without a bicycle facility

Can be applied on a roadway with, and can protect, on-street parking
Speed Limit Can be appropriate for any speed limit, provided an adequate shy distance is provided between the travel lane and the corner extension curb

Pennsylvania uses a maximum of 40 mph provided travel lanes are not narrowed; Delaware uses 35 mph
Vehicle Traffic Volume Can be appropriate at all levels of traffic volume; Pennsylvania permits daily volumes as high as 15,000 provided travel lanes are not narrowed
Emergency Route Can be appropriate along a primary emergency vehicle route or street that provides access to a hospital or emergency medical services (if appropriate turning radii can be provided)
Transit Route May not be appropriate where a bus turns along a transit route if an adequate turning radius cannot be provided; the stop bar on the opposite travel lane on the receiving leg of the intersection may need to be moved back in order to accommodate frequent transit vehicles making a turn; the number of turning transit vehicles and the total traffic volume on the receiving street are both factors when a corner extension is considered

An extended length corner extension could enable a bus stop landing area for both front and back transit bus doors, thereby eliminating the need for a bus to pull out of (and pull back into) traffic

A corner extension bus stop eliminates the need to remove on-street parking that would enable a transit vehicle to maneuver to and from the traditional curb
Access Route Typically not appropriate along a primary access route to a commercial or industrial site if an adequate turning radius cannot be provided; the number of large turning vehicles and the total traffic volume on the receiving street are both factors when a corner extension is considered
Grade Can be installed on a crest vertical curve only if there is adequate stopping sight distance or if appropriate warning signs are provided

Maximum grade should comply with local standards and criteria; Delaware uses a maximum grade of 6 percent

Figure 3.16.3. Corner Extension in Urban Setting. This figure contains a photograph with a focus on the corner extension. Near the bottom of the picture there is a tree planted at the curb. Further up the sidewalk on the corner extension there is a bench with people seated on it and a series of large, round planters. There is a stop sign at the intersection facing the camera. A four story building occupies the corner diagonally from the extension. The opposite corner has a set of shops.
Figure 3.16.3. Corner Extension in Urban Setting
(Source: Jennifer Rosales)

Figure 3.16.4. Corner Extension in Suburban Setting. This figures contains a photograph which shows a corner where two streets intersect. A corner extension is built out onto the street nearest the bottom of the picture. A stop sign is visible and there are several vehicles parked diagonally on the other street near the corner of a single story building. Palm trees grow in the lot opposite the house and a school can be seen in the distance.
Figure 3.16.4. Corner Extension in Suburban Setting
(Source: www.pedbikeimages.org / Michael Austin)

EFFECTS AND ISSUES

Effects and Issues – Corner Extension/Bulbout
Vehicle Speed Can slow traffic by funneling through narrower street opening than is provided in upstream cross-section; speeds likely to decrease slightly; amount of speed reduction depends on volume and distribution of traffic

Speeds are reduced on intersection approach and through intersection area

Shorter curb radius can slow turning vehicles; if large right-turning volume, could increase delay and lower speeds
Vehicle Volume Has little effect on traffic volumes; access and turns are maintained and traffic speeds are not changed dramatically
Pedestrian Safety and Mobility Shortens intersection crossing distance for a pedestrian; shorter distance reduces the potential for pedestrian-vehicle conflict and likely improves pedestrian safety

Provides additional queuing space for pedestrians at corner

Because corner extension is elevated above the vehicle travel lanes, improves line-of-sight for pedestrian at the corner and makes that pedestrian more visible to oncoming motorist; also enables pedestrian to stand at edge of parked vehicles, further increasing visibility

Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility Should not extend into a bicycle lane (see Figure 3.16.5)
Motorist Safety and Mobility Likely to have minimal effect on motorist mobility and safety

Presence of physical feature reduces possibility of illegal parking close to intersection
Emergency Vehicle Safety and Mobility Retains sufficient width to allow for continued easy flow of emergency vehicles

Shortened curb radius may require emergency vehicle turning at intersection to swing across centerline

Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility Retains sufficient width to allow for continued easy flow of large vehicles like combination trucks

Shortened curb radius may require large vehicle turning at intersection to swing across centerline

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property May require removal of some on-street parking immediately adjacent to intersection
Environment Can be used as a landscaping opportunity; many cities use bioswale curb extensions to capture stormwater (see Figure 3.16.6); if the corner extension includes a pedestrian crossing, the landscaping should be designed to not obstruct pedestrian visibility
Design Issues Relocation of curbing and pedestrian queuing area may require relocation of drainage features such as catch basins, concrete channels, valley gutters, inlets, and trench drains

May require relocation of above- and below-ground utilities

Figure 3.16.5. Corner Extension and Bicycle Lane. This figure contains a photograph of a street running from the bottom left to the top right. Another street forms an intersection running across the photo's centerline. A signpost can be seen on the corner extension extending into the street running top to bottom. A diamond shaped yellow sign depicts an icon of a person walking and a bicycle. Near the curb there is space for parallel parking and between the parking and the lane there is a separate bicycle lane. Crosswalks are visible running left to right at the intersection. A row of houses can be seen on the corner opposite.
Figure 3.16.5. Corner Extension and Bicycle Lane
(Source: Scott Batson)

Figure 3.16.6. Corner Extension with Bioswale. This figure contains a photograph focusing on a corner extension. The center of the extension contains a rectangular depression filled with grass and low bushes. To the left of this planting box there is a tree growing from another dedicated planting area. The section of the extension near the bottom of the photo has a ramp cut to street level. A white vehicle is parked parallel to the curb on the far side of the extension. A yellow taxi can be seen driving off camera towards the right side of the picture. A series of shops can be seen on the left hand side of the picture.
Figure 3.16.6. Corner Extension with Bioswale
(Source: Scott Batson)

ADDITIONAL DESIGN CONSIDERATIONS

The design of a corner extension needs to pay close attention to the existing drainage system because the gutter alignment will be altered (see Figure 3.16.7). A corner extension could necessitate a major utility relocation particularly if additional drainage inlets are required (see Figure 3.16.8).

A corner extension is typically constructed to a width of between 6 and 8 feet. It should be offset from the through traffic lane by 1.5 feet.

A sample design for a corner extension is presented in Figure 3.16.9.

Figure 3.16.7. Corner Extension with Realigned Gutter. This figure contains a photograph focusing on the right lane of a street running top to bottom in the picture and a corner extension following the right hand curb. The extension is surfaced with red brick. A gutter with a storm drain near the bottom of the picture is shown to illustrate how the path of the gutter has been adapted to follow the new curb. The curb extension is separated from a sidewalk by a strip of grass. A white picket fence parallels the right hand side of the walkway. A street sign is visible at the corner and there is a red brick house opposite.
Figure 3.16.7. Corner Extension with Realigned Gutter
(Source: Jeff Gulden)

Figure 3.16.8. Corner Extension with Drainage Structure Relocation. This figure contains a photograph of a street running from the bottom left to the center of the top edge. A sidewalk and corner extension dominate the bottom right hand quadrant of the picture. The corner extension is filled with rocks and small trees. Dark, one story buildings occupy the opposite corner of the intersection. This corner extension has a drainage structure in it.
Figure 3.16.8. Corner Extension with Drainage Structure Relocation
(Source: James R. Barrera)

Figure 3.16.9. Sample Design for Corner Extension. This figure contains a line drawing of an overhead view of an intersection. It is labeled Delaware Department of Transportation – Typical Corner Extension. The intersection divides the drawing into quadrants. The top left contains the text "Optional crosswalk lines as per DEMUTCD". A text box contains the text Sign Descriptions – OM Object Marker, L Left side of roadway, R Right side of roadway. The top right quadrant contains an arrow pointing to the sidewalk running left to right and a label "Sidewalk". The corner extension coming off of the corner has an arrow pointing to it and the text "OM3-R". The bottom right quadrant contains an arrow pointing to the center of the curve of the nearest extension and is labeled "Radius designed to accommodate design vehicles". The bottom left quadrant contains an arrow pointing to an icon, labeling it "OM3-R". The angle of the curb making up the corner extension is labeled as being forty-five degrees and an arrow shows the distance from curb to where the corner extension ends as being eight feet typically. In the right hand side of the street running left to right, a double headed arrow shows the width of the street from extension to extension to be twenty-four to twenty-eight feet typically.)
Figure 3.16.9. Sample Design for Corner Extension
(Source: Delaware Department of Transportation)

3.17 Choker

DESCRIPTION AND GENERAL PURPOSE

A curb extension is a horizontal extension of the curb into the street resulting in a narrower roadway section. This device may be used at either corner or midblock. A curb extension located midblock is called a choker. A curb extension located at an intersection is called a corner extension or bulbout [provide link to section 3.16].

A choker is the narrowing of a roadway through the use of curb extensions or roadside islands (see Figure 3.17.1). It can be created by a pair of curb extensions at a midblock location that narrows the street by widening the sidewalk or planting strip at that location. A choker can also be created through the use of roadside islands. This narrowing is intended to discourage motorist speeding and to reduce vehicle speeds in general.

Within a choker on a two-way, two lane roadway, vehicles are able to pass each other without conflict. But the narrower cross-section lowers the margin of error for motorists who, as a result, tend to moderate their speed. In some applications, a double-lane choker is combined with a median island as a means to reduce the possibility of opposing vehicle conflicts.

A one-lane choker forces two-way traffic to take turns going through the pinch point. If the roadway is narrowed to a single lane, the lane can be either parallel to the initial roadway alignment or angled to the alignment. The former is called a parallel choker, the latter an angled choker, twisted choker, or angle point (see Figure 3.17.2).

A choker can be located at any spacing desired for traffic calming. A choker is often combined with on-street parking to create a protected parking bay.

Landscaping on a choker can make the traffic calming feature attractive and can make it more visible to the motorist.

A choker may be a good location to place a midblock crosswalk (either level with the roadway or as a raised crosswalk) because it shortens the distance a pedestrian walks on the travelway.

[Other terms for choker include pinch point, midblock narrowing, midblock yield point, constriction, or edge island. If the choker is marked with a crosswalk, it is sometimes called a safe cross.]

[Four field studies of 12 chokers measured reductions between 1 and 4 mph for 85th percentile speeds (Source: FHWA, Engineering Speed Management Countermeasures: A Desktop Reference of Potential Effectiveness in Reducing Speed, July 2014) http://www.safety.fhwa.dot.gov/speedmgt/ref_mats/eng_count/2014/reducing_speed.cfm]

Figure 3.17.1. Choker Schematic. This figure contains a line drawing of a two lane street divided by a double line from an overhead view. Three houses line each side of the street. Halfway along the street a pair of patterned curb extensions extend into and narrow the street with a choker. There are two vehicles in each lane; one near the northern curb extension, one in that same lane near the right hand edge of the picture, one approaching the southern curb extension, and one near the right hand edge of the picture.
Figure 3.17.1. Choker Schematic
(Source: Delaware Department of Transportation)

Figure 3.17.2. Angled Choker. This figure contains a photograph of a street running top to bottom near the center of the picture with an angled choker. A rounded curb extension on each side of the road causes it to narrow and angle from left to right. The extensions are covered in grass and are separated from nearby houses by sidewalk. White reflector posts follow the curved portion of each extension. A signpost on the right side of the street contains a diamond shaped yellow sign with a black arrow pointing down and to the left.
Figure 3.17.2. Angled Choker
(Source: Dan Burden)

APPROPRIATE APPLICATION

Appropriate Application – Choker
Type of Street Appropriate for an arterial, collector, or local street – whether in an urban or suburban setting (see Figures 3.17.3 and 3.17.4)
Intersection or Roadway Segment Applicable only midblock; if placed at an intersection, considered a corner extension/bulbout [provide link to section 3.16]
Roadway Cross-Section Can be used on a one-lane, one-way and two-lane, two-way street

Most easily installed on a roadway with an urban cross-section (i.e., curb and gutter)

Can be applied both with and without a bicycle facility

Can be applied on a street with, and can protect, on-street parking
Speed Limit Can be appropriate for any speed limit, provided an adequate shy distance is provided between the travel lane and the choker curb; Pennsylvania uses a maximum of 40 mph provided travel lanes are not narrowed; Delaware uses 35 mph
Vehicle Traffic Volume Can be appropriate at all levels of traffic volume
Emergency Route Can be appropriate along a primary emergency vehicle route or street that provides access to a hospital or emergency medical services
Transit Route Can be appropriate along a bus transit route
Access Route Can be appropriate along a primary access route to a commercial or industrial site
Grade Can be installed on a crest vertical curve only if there is adequate stopping sight distance or if appropriate warning signs are provided

Maximum grade should comply with local standards and criteria; Delaware uses a maximum grade of 6 percent

Figure 3.17.3. Choker in Urban Commercial Setting. This figure contains a photograph of a two lane street. The street runs from top left to bottom right of the picture. Palm trees line each side of the street. A crosswalk runs across the bottom of the picture. A choker has been used to narrow the street at the crosswalk. Both crosswalk and sidewalk are made of patterned brick. Two older pedestrians have just crossed the street from right to left.
Figure 3.17.3. Choker in Urban Commercial Setting
(Source: www.pedbikeimages.org / Dan Burden)

Figure 3.17.4. Choker in Suburban Residential Setting. This figure contains a photograph of a broad two lane residential street divided by a double yellow line. The street runs from bottom left to top right, curving sharply to the right as it gets to the top. At the halfway point, a choker has been used to narrow the road. Each extension is landscaped with grass, shrubs, and trees. Sidewalk separate the houses on each side from the curbs.
Figure 3.17.4. Choker in Suburban Residential Setting
(Source: Scott Wainwright)

EFFECTS AND ISSUES

Effects and Issues – Choker
Vehicle Speed Can slow traffic by funneling through narrower street opening than is provided in upstream cross-section; traffic speeds likely to decrease slightly (see Figure 3.17.5)

Amount of speed reduction depends on volume and distribution of traffic; reduction is lessened when (1) the volume of traffic is significantly higher in one direction than the other or (2) volumes are so low that the likelihood of a motorist encountering an opposing motorist within the narrowed area is low
Vehicle Volume Has little effect on traffic volumes
Pedestrian Safety and Mobility Shortens street crossing distance for a pedestrian; shorter distance reduces potential for pedestrian-vehicle conflict and likely improves pedestrian safety (see Figure 3.17.6)

Because it is elevated above the vehicle travel lanes, improves line-of-sight for a pedestrian at the crossing and makes that pedestrian more visible to an oncoming motorist

Refer to Module 6 for additional discussion
Bicyclist Safety and Mobility May reduce travelway width and force bicyclist and motor vehicle to share travel lane; if the vehicle volume is high, use of shared lane markings (sometimes known as a sharrow) and "bike may use full lane" signage could be necessary and appropriate
Motorist Safety and Mobility Likely to have minimal effect on motorist mobility and safety Minimal impact on motorist comfort

Can serve as protection for downstream on-street parked vehicles
Emergency Vehicle Safety and Mobility Retains sufficient width to allow for continued flow of emergency vehicles

Refer to Module 5 for additional discussion
Large Vehicle Safety and Mobility Retains sufficient width to allow for continued flow of large vehicles like combination trucks

Refer to Module 5 for additional discussion
Accessibility of Adjacent Property May require removal of some on-street parking; therefore, may slightly reduce accessibility of adjacent property
Environment Can be used as landscaping opportunity; if the choker includes a pedestrian crossing, the landscaping should be designed to not obstruct pedestrian visibility
Design Issues Relocation of curbing may require relocation of drainage features such as catch basins, concrete channels, valley gutters, inlets, and trench drains

May require relocation of above- and below-ground utilities

Where the crown of a street is steep, a choker may actually go "uphill" because the new curb is higher than the original curb; this has the potential to cause drainage problems both at the curb and on the sidewalk

Figure 3.17.5. Choker with Passing Traffic. his figure contains a photograph of an undivided two lane street running from the bottom right to near the top left of the picture. Curb extensions, detached from the sidewalks and outlined in white stripes, dominate the center of the photograph. A white car travelling towards the camera and a gray car travelling away are passing through the choker at the same time.  A car is parallel parked in the opposite lane, pointed away from the camera after the chocker. Trees are scattered around the sides of the street and a  tan building can be seen in the distance.
Figure 3.17.5. Choker with Passing Traffic
(Source: James R. Barrera)

Figure 3.17.6. Choker with Pedestrian Crosswalk. This figure contains a photograph of a two lane street running from bottom right to top left. A choker is used to narrow the street in the center of the photo for a crosswalk. The extensions are landscaped with grass. A stop sign can be seen on the right hand extension, near a sidewalk. Cars are parallel parked on the right hand side of the street. On the far side of those cars there is a parking lot. On the left hand side of the street, on the extension near the intersection, there is a small green sign for bike rentals.
Figure 3.17.6. Choker with Pedestrian Crosswalk
(Source: Shawn Leight)

ADDITIONAL DESIGN CONSIDERATIONS

A choker can be created by either curb extensions or edge islands. A curb extension offers more opportunity for aesthetic enhancements through landscaping. But an edge island leaves existing drainage channels open, making it possible to provide a bicycle bypass lane on a street without curbside parking.

The curb extension for the choker is typically constructed to a width of between 6 and 8 feet (see Figure 3.17.7). It should be offset from the through traffic lane by 1.5 feet.

In order to comply with the International Fire Code, 20 feet is the recommended space for a fire truck with aerial bucket or ladder so the outriggers can be set up. This width also permits smooth personnel operation around the vehicle during an emergency call. For the passage of a fire truck, 12 feet is the minimum and 14 feet is recommended for the narrowest roadway section.

On a street with little bicycle traffic or a low motor vehicle volume, the probability is low that a vehicle and bicycle will meet at the choker. In that case, no special accommodation is likely necessary for bicyclists. However, on a street with a bicycle lane or on a street with higher volumes, either (1) provide a bypass lane for a bicyclist, separated from the main travel lane by a curb extension or (2) provide shared lane markings (sometimes known as a sharrow) and "bike may use full lane" signage.

A midblock location near a streetlight is preferred for a choker.

Edge line tapers should conform to the MUTCD taper formulas.

Any curb extension or edge island should include signs compliant with MUTCD guidance.

The length of a choker island should be at least 20 feet, the length of a single car. A choker may extend toward the centerline beyond any parking lane. A sample design for a choker is presented in Figure 3.17.8.

Figure 3.17.7. Choker Adjacent to On-Street Parking. This figure contains a photograph of a two lane street divided by a double yellow line, using a choker at a crosswalk. The left hand side of the street shows available parallel parking near two parking meters. Buildings and off street parking can be seen across the street. The curb extensions are landscaped with grass on either side of the ramps to the sidewalk.
Figure 3.17.7. Choker Adjacent to On-Street Parking
(Source: Creative Commons / Richard Drdul)

Figure 3.17.8. Sample Design for Choker. The figure contains a line drawing of an overhead view of a two lane street divided using a double line and is labeled Delaware Department of Transportation – Typical Choker. The street runs right to left and uses a choker at its midpoint to narrow the lanes. The upper half of the diagram has a text box containing the text "Sign Description – R4-7 Keep Right, OM1-3 Object Marker". And oval shows an exploded view of optional pavement markers along taper. The extension on the supper lane is labeled "Optional Patterned Pavement" A one to two inch drainage channel between the extension and the curb is labeled. The existing curb is labeled as is the edge line that runs around the extension. On the lower lane, the diagram labels the taper length of the edge line per the DEMUTCD. Signs on both extensions are labeled OM1-3.
Figure 3.17.8. Sample Design for Choker
(Source: Delaware Department of Transportation)

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