Intersection Safety Strategies Brochure

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Aerial photograph of a well-marked signalized intersection treated with cross walks.

KEY TO THE INTERSECTION SAFETY STRATEGY GUIDE SHEETS “Objectives and Strategies for Improving Safety at Unsignalized and Signalized Intersections”

Unsignalized Intersection Strategies

A. Improve Management of Access

B. Reduce Conflicts Through Geometric Design Improvements

C. Improve Sight Distance

D. Improve Availability of Gaps in Traffic and Assist Drivers in Judging Gaps

E. Improve Driver Awareness on Approaches

F. Choose Appropriate Intersection Traffic Control

G. Improve Compliance with Traffic Control Devices and Traffic Laws

H. Reduce Operating Speeds on Approaches

I. Guide Motorists More Effectively on Approaches

Signalized Intersection Strategies

A. Traffic Control and Operational Improvements

B. Geometric Improvements

C. Improve Sight Distance

D. Improve Driver Awareness

E. Improve Driver Compliance

F. Improve Access Management

G. Improve Safety through Other Infrastructure Treatments

Key to the Brochure

Time frame:

Time frames will naturally vary based on numerous factors (agency procedures, number of stakeholders, need for additional right-ofway). The scale is meant as a general guide. One circle indicates a short time frame for implementation perhaps in as little as a few months or up to 1 year. Example short term strategies include signage improvements, signal timing changes, and sight distance improvements. Two circles indicates a medium time frame of 1-2 years. Example medium term strategies include channelization improvements, system-wide signal improvements, and minor geometric improvements. Three circles indicates a longer time frame of over 2 years. These strategies will typically require major construction or right-of-way acquisition.

Costs:

Costs will also vary considerably and are affected by local conditions. Costs are ranked as: low, moderate, moderate to high, and high. The scale is meant to reflect costs relative to the other strategies described in the category (signalized or unsignalized).

Effectiveness:

This section will discuss any research or evaluations that have been done to ascertain the effectiveness of the particular strategy. Three descriptors are used to identify to what degree the strategy has been evaluated:

Proven: Those strategies that have been used in one or more locations and for which properly designed evaluations have been conducted that show it to be effective. These strategies may be employed with a good degree of confidence, but with the understanding that any application can lead to results that vary significantly from those found in previous evaluations. Crash reduction factors reported are typically based on valid research methods.

Tried: Those strategies that have been implemented in a number of locations and may even be accepted as standards or standard approaches, but for which there have not been found valid evaluations. These strategies, while frequently or even generally used, should be applied with caution; users should carefully consider the attributes cited in the guide and relate them to the specific conditions for which they are being considered. There can be some degree of assurance that implementation will not likely have a negative impact on safety and will very likely have a positive one. Crash reduction factors reported are not necessarily based on valid research methods and should be used with caution.

Experimental: Those strategies that have been suggested and that at least one agency has considered sufficiently promising to try on a small scale in at least one location. These strategies should be considered only after the others have been determined to be inappropriate or unfeasible. Even where they are considered, their implementation should initially occur using a very controlled and limited pilot study that includes a properly designed evaluation component.

This brochure is a quick reference to the countermeasures described in the NCHRP Report 500 volumes on reducing crashes at unsignalized (Volume 5) and signalized (Volume 12) intersections and is a supplement to individual guide sheets for each of the 77 countermeasures. These documents describe and illustrate the countermeasures in greater detail.

Unsignalized Intersection Safety Strategies


COST
Safety Concern: High frequency of right-angle crashes attributed to: Low Moderate Moderate-High High
nearby driveways A2, B12, C1, C2, C4 A1 B8 empty cell
traffic from minor street B12, C1, C2, C4, D2 D1 B8 B13, F3
skewed intersection empty cell empty cell empty cell B16, C3, F3
poor sight distance C1, C2, C4, H3 D1 empty cell C3, F3
drivers misjudging gaps D2, H3 D1 empty cell F3
not enough gaps for drivers D3 empty cell empty cell B14, F3
driver unaware of intersection E1, 5-E9, E10, E11 E3 empty cell empty cell
nighttime conditions E10 empty cell E2 empty cell
failure to yield at stop or yield sign E1, E4-E9, E11 G1 empty cell F3
possible signal location empty cell empty cell empty cell F1, F3
heavy but balanced traffic flow F2 empty cell empty cell F3
speed differentials of vehicles H3 H1, H2 empty cell F3
Safety Concern: High frequency of rear-end crashes attributed to: empty cell empty cell empty cell empty cell
left turning vehicles hit from behind B4 B1, B2 empty cell F3
left opposing vehicles hit from behind empty cell empty cell B3 F3
trucks and RVs entering divided highway empty cell B5 empty cell empty cell
speed differential of entering vehicles empty cell B6, B9 empty cell F3
right turning vehicles hit from behind empty cell B6, B7 empty cell B16, F3
appoaching vehicles hit from behind empty cell B10 empty cell empty cell
no left turn lane and high opposing traffic B11, B12 empty cell empty cell B13
driver unaware of intersection E1, E5-E9, E10, E11 E3 empty cell empty cell
nighttime conditions E8, E10 empty cell E2 empty cell
speed differentials of vehicles H3 H1, H2 empty cell F3
Safety Concern: High frequency of left-turn crashes attributed to: empty cell empty cell empty cell empty cell
left turn vehicles hit by opposing traffic C2 B1, B17 B3 B15, F3
trucks and/or RVs entering divided highway empty cell B5 empty cell empty cell
no left turn lane and high opposing traffic B11, B12 B17 empty cell B13
nighttime conditions E10 empty cell E2 empty cell
heavy but balanced traffic flow F2 empty cell empty cell F3
Poor sight distance C2, B11, B12 B17 empty cell B13
Safety Concern: High frequency of sideswipe crashes attributed to: empty cell empty cell empty cell empty cell
speed differential of entering vehicles empty cell B9 empty cell F3
vehicles within intersection I1, I2 empty cell empty cell empty cell
vehicles approaching intersection I3 empty cell empty cell empty cell
Safety Concern: High frequency of run off road crashes: empty cell empty cell empty cell empty cell
approaching intersection empty cell B10 empty cell empty cell
Safety Concern: High frequency of pedestrian/bicycle crashes: empty cell empty cell empty cell empty cell
at the intersection empty cell empty cell B18, H2 empty cell
Safety Concern: Address overall safety issues: empty cell empty cell empty cell empty cell
violation of traffic laws G2 empty cell empty cell empty cell
Note: Counter measures indicated on the table are possible treatments for individual crash problems. Implementation should be based on individual circumstances and studies.

CATEGORY A: IMPROVE MANAGEMENT OF ACCESS

Photo of a business on a corner where one side of the parking area is railed in to prevent access to the road from that side. A1 – Implement driveway closures/relocations (HTML | PDF). WHERE TO USE – Unsignalized intersections with high crash frequencies related to driveways adjacent to the intersection. Generally, driveways within 250 feet of the intersection are the greatest concern. Time: Short. Effectiveness: Tried

One photo showing a barrier island with a right turn only design and another photo showing lane delineator rods on the centerline that prevent traffic from turning.A2 – Implement driveway turn restrictions (HTML | PDF). WHERE TO USE – Driveways located near unsignalized intersections that experience high crash frequencies but that cannot practically be closed or relocated. Time: Short. Effectiveness: Tried.

CATEGORY B: REDUCE CONFLICTS THROUGH GEOMETRIC DESIGN IMPROVEMENTS

Photograph of a T-intersection with a turn lane provided for left-turning traffic.B1 – Provide left-turn lanes at intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with a high frequency of crashes resulting from the conflict between (1) vehicles turning left and following vehicles and (2) vehicles turning left and opposing through vehicles. Time: Medium. Effectiveness: Proven.

Photograph of a rural intersection with very long left and right turn lanes. B2 – Provide longer left-turn lanes at intersections (HTML | PDF).WHERE TO USE – Unsignalized intersections with existing leftturn lanes that are not long enough to store all left-turning vehicles and have a high frequency of rear-end crashes resulting from the conflict between vehicles waiting to turn left and following vehicles. Time: Medium. Effectiveness: Tried.

Photograph of a road design where the left turn lanes are offset from the through lanes, allowing left turning vehicles going in each direction to see oncoming traffic. B3 – Provide offset left-turn lanes at intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with a high frequency of crashes between vehicles turning left and opposing through vehicles, as well as rear-end crashes between through vehicles on the opposing approach. Also at intersections on divided highways with medians wide enough to provide the appropriate offset but can be implemented on approaches without medians if sufficient width exists. Time: Medium. Effectiveness: Tried.

Photograph of a T-intersection with a bypass lane B4 – Provide bypass lanes on shoulders at T-intersections (HTML | PDF). WHERE TO USE – At three-legged unsignalized intersections on two-lane highways with moderate through and turning volumes, especially intersections that have a pattern of rearend collisions involving vehicles waiting to turn left from the highway. Time: Short. Effectiveness: Tried.

Photo of a vehicle turning into a left turn acceleration lane. B5 – Provide left-turn acceleration lanes at divided highway intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections on divided highways that experience a high proportion of rear-end crashes related to the speed differential caused by vehicles turning left onto the highway. Also where intersection sight distance is inadequate or where there are high volumes of trucks or recreational vehicles entering the divided highway. Time: Medium. Effectiveness: Tried.

Photograph of an unsignalized intersection with a long right turn lane off the main road onto a secondary road. B6 – Provide right-turn lanes at intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with a high frequency of rear-end crashes resulting from conflicts between (1) vehicles turning right and following vehicles and (2) vehicles turning right and through vehicles coming from the left on the cross street. Time: Medium. Effectiveness: Proven.

Photograph of a rural unsignalized intersection with a very long right lane. B7 – Provide longer right-turn lanes at intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with an existing right-turn lane that is not long enough to store all right-turning vehicles and that are experiencing a high frequency of rear-end crashes resulting from the conflict between vehicles waiting to turn right and following vehicles. Time: Medium. Effectiveness: Tried.

Photograph of an intersection with an offset right turn lane. B8 – Provide offset right-turn lanes at intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with a high frequency of crashes between vehicles on the minor road that are turning left, turning right, or proceeding straight through, and vehicles on the major road. Time: Medium. Effectiveness: Tried.

Photograph of an intersection with a rural highway. Right turning vehicles entering the highway have a lengthy stretch of acceleration lane to the right of the highway through lanes. B9 – Provide right-turn acceleration lanes at intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections that experience a high proportion of rear-end and/or sideswipe crashes related to the speed differential caused by vehicles making a rightturn maneuver onto the highway. Time: Medium. Effectiveness: Tried.

Photos of rural unsignalized stop-control intersections on roadways with no shoulders. B10 – Provide full-width paved shoulders in intersection areas (HTML | PDF). WHERE TO USE – Unsignalized intersections on divided highways with no shoulder or shoulder widths less than 8 feet that experience a high proportion of run-off-road crashes as a result of avoidance maneuvers or a high proportion of rearend crashes that could have been avoided had a full-width paved shoulder been provided. Time: Medium. Effectiveness: Tried.

Photograph of a downtown area with posted variable lane use signs that indicate when restrictions on use of a continuous center turn lane are in place. B11 – Restrict or eliminate turning maneuvers by signing (HTML | PDF). WHERE TO USE – Unsignalized intersections with patterns of crashes related to particular turning maneuvers where it is impractical to reduce that pattern of crashes by improving sight distance or providing a left-turn or shoulder bypass lane. Time: Short. Effectiveness: Tried.

Photo of an unsignalized intersection where left turns are channelized for both approaching and oncoming traffic. B12 – Restrict or eliminate turning maneuvers by providing channelization or closing median openings (HTML | PDF). WHERE TO USE – Unsignalized intersections with patterns of crashes related to particular turning maneuvers where it is impractical to reduce that pattern of crashes by improving sight distance or providing a left-turn or shoulder bypass lane. Also, at locations where it is possible to restrict or eliminate turning maneuvers by providing channelization or by closing the median opening. Time: Short. Effectiveness: Tried.

Photograph of a T-intersection treated with a channelized right turn lane, one-way signs, and a closed median with reflective markers and a raised curb. B13 – Close or relocate "high-risk" intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with high levels of intersection-related crashes that other strategies have not been successful in reducing or for which other strategies are not considered appropriate. Also at locations where a particular strategy such as installing a turn lane or increasing sight distance is impractical at the current location, but could be applied if the intersection were moved. Time: Long. Effectiveness: Tried.

Diagram showing the realignment of a four-legged intersection to create two T-intersections. B14 – Convert four-legged intersections to two T-intersections (HTML | PDF). WHERE TO USE – Unsignalized four-legged intersections with very low through volumes on the cross street. Time: Medium. Effectiveness: Tried.

Diagram showing the realignment of two T-intersections to create a four-legged intersection. B15 – Convert offset T-intersections to four-legged intersections (HTML | PDF). WHERE TO USE – Unsignalized offset T-intersections where through volumes on the cross street are very high. Time: Medium. Effectiveness: Tried.

Photo shows how two roads that met at an X-like angle was realigned to so that the roads meet at a more traditional 90 degree angle. B16 – Realign intersection approaches to reduce or eliminate intersection skew (HTML | PDF). WHERE TO USE – Unsignalized intersections with a high frequency of crashes resulting from insufficient intersection sight distance and awkward sight lines at a skewed intersection. Time: Medium. Effectiveness: Proven.

Photograph of an intersection where left turns are prohibited. To complete a left turn, drivers must use the right lane exit, turn left at the minor intersection, and subsequently travel through the major intersection. B17 – Use indirect left-turn treatments to minimize conflicts at divided highway intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with operational and safety problems that can be traced to difficulties of accommodating left-turn demand. Time: Medium. Effectiveness: Tried.

Photo of a two-lane road in a wooded area with pavement markings indicating a bike and pedestrian crossing ahead. B18 – Improve pedestrian and bicycle facilities to reduce conflicts between motorists and nonmotorists (HTML | PDF). WHERE TO USE – Unsignalized intersections that experience crashes involving pedestrians and/or bicyclists with motor vehicles or that have the potential for such crashes. Time: Medium. Effectiveness: Tried/Proven.

CATEGORY C: IMPROVE SIGHT DISTANCE

Photo dipicting overgrown median landscaping blocking the view of turning drivers. C1 – Clear sight triangles on stop- or yield-controlled approaches to intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with restricted sight distance and patterns of crashes related to lack of sight distance, where sight distance can be improved by clearing roadside obstructions without major construction. Time: Short. Effectiveness: Tried.

Photograph showing an overgrown median that may hide oncoming vehicles from turning traffic. C2 – Clear sight triangles in the medians of divided highways near intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections on divided highways with (a) fixed sight obstructions in the median near the intersection and (b) patterns of crashes related to the lack of sight distance. Time: Short. Effectiveness: Tried.

Diagram shows that variations in the verticle alignment of perpendicular streets can have a significant impact on sight distance; the greater the verticle grade the less the sight distance between perpendicular vehicles. Conversely, a decreased or flattened grade increases sight distance. C3 – Change horizontal and/or vertical alignment of approaches to provide more sight distance (HTML | PDF). WHERE TO USE – Unsignalized intersections with restricted sight distance due to horizontal and/or vertical geometry and with patterns of crashes related to that lack of sight distance that cannot be ameliorated by less expensive methods. Time: Long. Effectiveness: Tried.

Photo depicts a painted box on the roadway at the corner of a neighborhood intersection that prohibits vehicles from parallel parking within it so that sight distance will not be blocked for for left turning vehicles. C4 – Eliminate parking that restricts sight distance (HTML | PDF). WHERE TO USE – Unsignalized intersections with restricted sight distance due to parking. Time: Short. Effectiveness: Tried.

CATEGORY D: IMPROVE AVAILABILITY OF GAPS AND ASSIST DRIVERS IN JUDGING GAPS

Photo of a sign that warns drivers that traffic is entering the roadway from the right when the attached light is flashing. D1 – Provide an automated real-time system to inform drivers of the suitability of available gaps for making turning and crossing maneuvers (HTML | PDF). WHERE TO USE – Unsignalized intersections with a high frequency of right-angle collisions due to restricted sight distance. Time: Medium. Effectiveness: Experimental.

Diagram depicts an intersection where through traffic does not stop, but perpendicular side street traffic does. The intersection is characterized by 'STOP' markings on the pavement for sidestreet traffic, STOP signs at the side streets, signs advising side street traffic to look Left-Right-Left before pulling out, signs advising through traffic of entering vehicles, and pavement markings advising through traffic of the speed limit. D2 – Provide innovative signs and markings to assist drivers in judging the suitability of available gaps for making turning and crossing maneuvers (HTML | PDF). WHERE TO USE – Unsignalized intersections where crash data shows a high occurrence of crashes where vehicles on secondary roadways intersecting at grade misjudge the gap between approaching vehicles. Time: Medium. Effectiveness: Experimental.

Photograph shows a busy T intersection in advance of a signalized intersection. D3 – Retime adjacent signals to create gaps at stopcontrolled intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections (between signalized intersections) with a high frequency of right-angle or turningrelated crashes due to a lack of sufficient gaps in through traffic on the major road. Time: Short. Effectiveness: Tried.

CATEGORY E: IMPROVE DRIVER AWARENESS

Photos of rural roadside signs indicating an intersection ahead and providing the name of the cross street. E1 – Improve visibility of intersections by providing enhanced signing and delineation (HTML | PDF). WHERE TO USE – Unsignalized intersections that are not clearly visible to approaching motorists, particularly approaching motorists on the major road. The strategy is particularly appropriate for intersections with patterns of rear-end, rightangle, or turning crashes related to lack of driver awareness of the presence of the intersection. Time: Short. Effectiveness: Tried.

Photo of an unsignalized rural intersection treated with pole and mast arm lights. E2 – Improve visibility of the intersection by providing lighting (HTML | PDF). WHERE TO USE – Unsignalized, unlit intersections with substantial patterns of nighttime crashes. In particular, patterns of rear-end, right-angle, or turning crashes on the major-road approaches to an unsignalized intersection may indicate that approaching drivers are unaware of the presence of the intersection. Time: Medium. Effectiveness: Proven.

Photgraph of a T intersection where the cross street contains a chanellizing island between the two opposing lanes of traffic on the cross street that serves to separate vehicles turning onto the cross street from the mainline from those vehicles entering the mainline from the cross street. E3 – Install splitter islands on the minor-road approach to an intersection (HTML | PDF). WHERE TO USE – Minor road approaches to unsignalized intersections where the presence of the intersection or the stop sign is not readily visible to approaching motorists. The strategy is particularly appropriate for intersections where the speeds on the minor road are high. Time: Medium. Effectiveness: Tried.

Photo depicting the use of a wide stop bar on the minor approach to an intersection within a horizontal curve. E4 – Provide a stop bar (or provide a wider stop bar) on minor-road approaches (HTML | PDF). WHERE TO USE – Approaches to unsignalized intersections having traffic control devices that are not currently being recognized by some approaching motorists. Locations should be identified by patterns of crashes related to lack of driver recognition of the traffic control device (e.g., right-angle crashes related to stop sign violations). Time: Short. Effectiveness: Tried.

Photo of a four-way stop intersection treated with oversize stop signs. E5 – Install larger regulatory and warning signs at intersections (HTML | PDF). WHERE TO USE – Approaches to unsignalized intersections with patterns of rear-end, right-angle, or turning collisions related to lack of driver awareness of the presence of the intersection. Time: Short. Effectiveness: Tried.

Photograph of rumble strips on the approach to an intersection. E6 – Call attention to the intersection by installing rumble strips on intersection approaches (HTML | PDF). WHERE TO USE – Approaches to unsignalized intersections with traffic control devices that are not currently being recognized by some approaching motorists. Locations should be identified by patterns of crashes related to lack of driver recognition of the traffic control device (e.g., right-angle crashes related to stop sign violations). Rumble strips should be considered only after an adequate trial of less intrusive treatments. Time: Short. Effectiveness: Tried.

Depiction of a cross street intersecting a divided highway at a T-intersection. The pavement markings on the divided highway do not stop at the opening for the median and cross street, but continue across the median opening. E7 – Provide dashed markings (extended left edgelines) for major-road continuity across the median opening at divided highway intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections on divided highways. The strategy is particularly appropriate for intersections with patterns of rear-end, right-angle, or turning crashes related to lack of awareness by the driver on the minor road to the presence of the intersection. Time: Short. Effectiveness: Tried.

Photograph of STOP signs mounted on both a post and the mast arm it supports above a roadway. E8 – Provide supplementary stop signs mounted over the roadway (HTML | PDF). WHERE TO USE – Unsignalized intersections with patterns of right-angle crashes related to lack of driver awareness of the presence of the intersection. In particular, it might be appropriate to use this strategy at the first stop-controlled approach (possibly of a series) located on a long stretch of highway without any required stops, or at an intersection located after a sharp horizontal curve. Time: Short. Effectiveness: Tried.

Photograph of pavement marking advising drivers of a STOP sign ahead. E9 – Provide pavement markings with supplementary messages, such as STOP AHEAD (HTML | PDF). WHERE TO USE – Unsignalized intersections with patterns of rear-end, right-angle, or turning crashes related to lack of driver awareness of the presence of the intersection. Time: Short. Effectiveness: Tried.

Photo of a stop sign that is leaning to the side, is scarred, is not reflective, and is surrounded by unmowed vegetation. E10 – Provide improved maintenance of stop signs (HTML | PDF). WHERE TO USE – All stop-controlled intersections. Time: Short. Effectiveness: Tried.

Photograph of flashing beacons suspended overhead at a stop controlled intersections. E11 – Install flashing beacons at stop-controlled intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with patterns of right-angle crashes related to lack of driver awareness of the intersection on an uncontrolled approach and lack of driver awareness of the stop sign on a stop-controlled approach. Time: Short. Effectiveness: Tried.

CATEGORY F: CHOOSE APPROPRIATE INTERSECTION TRAFFIC CONTROL

Photograph of an ingress/egress on a one way road with left turn ingress from the mainline prohibited by delineator posts. The egress is also channelized to force exiting traffic to the right. F1 – Avoid signalizing through roads (HTML | PDF). WHERE TO USE – Medium- to high-volume unsignalized intersections where installation of signals is being considered. Before a decision to install a signal is made, adequate consideration should be given to less restrictive forms of traffic control. Time: Long. Effectiveness: Tried.

Photograph of a four-way stop sign and intersection in a neighborhood. F2 – Provide all-way stop-control at appropriate intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with patterns of right-angle and turning crashes and moderate and relatively balanced volumes on the intersection approaches. Time: Short. Effectiveness: Proven.

Photograph of a roundabout at the center of an intersection in a neighborhood. F3 – Provide roundabouts at appropriate locations (HTML | PDF). WHERE TO USE – Unsignalized intersections that are experiencing right-angle, rear-end, and turning crashes. Roundabouts are appropriate at most intersections, and at intersections with large traffic delays roundabouts are oftentimes a superior alternative to signalization. Roundabouts can also be very effective at intersections with complex geometry (e.g., more than four approach roads) and intersections with frequent left-turn movements. Time: Long. Effectiveness: Proven.

CATEGORY G: IMPROVE COMPLIANCE WITH TRAFFIC CONTROL DEVICES AND TRAFFIC LAWS

Blurred photograph of a vehicle moving past a STOP sign without stopping. G1 – Provide targeted enforcement to reduce stop sign violations (HTML | PDF). WHERE TO USE – Unsignalized intersections where stop sign violations and patterns of crashes related to stop sign violations have been observed. Crash types potentially related to stop sign violations include right-angle and turning collisions. Time: Short. Effectiveness: Tried.

Collage of images, including a screenshot of a web page, a brochure, and a photo of a device that shows both the posted speed limit and the actual speed of a vehicle as it approaches the device. G2 – Provide targeted public information and education on safety problems at specific intersections (HTML | PDF). WHERE TO USE – Jurisdictions that have experienced a large number of safety problems at unsignalized intersections. Time: Short. Effectiveness: Tried.

CATEGORY H: REDUCE OPERATING SPEEDS

Photograph of a speed detection radar device. H1 – Provide targeted speed enforcement (HTML | PDF). WHERE TO USE – Unsignalized intersections where speed violations and patterns of crashes related to speed violations are observed. Crash types potentially related to speed violations include right-angle, rear-end, and turning crashes. Time: Short. Effectiveness: Proven.

Photo of a neighborhood intersection treated with bulb outs and painted crosswalks. H2 – Provide traffic calming on intersection approaches through a combination of geometrics and traffic control devices (HTML | PDF). WHERE TO USE – Specific approaches to unsignalized intersections that are experiencing crash types potentially related to speed violations, specifically right-angle, rear-end, and turning collisions. Time: Medium. Effectiveness: Proven.

Photo of a rural roadway with a clearly posted speed limit sign. H3 – Post appropriate speed limit on intersection approaches (HTML | PDF). WHERE TO USE – Unsignalized intersections experiencing a high frequency of speed related crashes. Time: Short. Effectiveness: Tried.

CATEGORY I: GUIDE MOTORISTS MORE EFFECTIVELY

Diagram of an intersection containing a curved, dashed line that connects the double yellow line that defines the left edge of the left turn lane to the double yellow line of the perpendicular road onto which left turning traffic flows. I1 – Provide turn path markings (HTML | PDF). WHERE TO USE – Complex unsignalized intersections with a high frequency of crashes related to turning vehicle positioning (e.g., sideswipe crashes). Time: Short. Effectiveness: Tried.

Photo shows a double yellow line bisecting a median, providing delineation for vehicles crossing the median or turning across the median. I2 – Provide a double yellow centerline on the median opening of a divided highway at intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections on divided highways that are experiencing a high degree of crashes caused by sideby- side queuing and angle stopping within the median area. Time: Short. Effectiveness: Tried.

Photo of lane assignment signs on a mast arm above the roadway in advance of a signal. Signs indicate which lane vehicles should be in to reach specified routes. I3 – Provide lane assignment signing or marking at complex intersections (HTML | PDF). WHERE TO USE – Unsignalized intersections with a high frequency of crashes caused by driver indecision in lane assignment. Time: Short. Effectiveness: Tried.

Signalized Intersection Safety Strategies

COST
Safety Concern: High frequency of right-angle crashes attributed to: Low Moderate Moderate-High High
nearby driveways F1, F2
traffic from cross street A2, A3 E2, E3
skewed intersection    B4, B5, C2
poor sight distance A1, C1, G5 G4  B4, B5, C2
drivers misjudging gaps A1
not enough gaps for drivers A1 A4
driver unaware of intersection D1, D2   B4, C2
nighttime conditions D1, D2
right turning vehicles hit from side A3, C1, G5 B2, G4
Safety Concern: High frequency of rear-end crashes attributed to:
left turning vehicles hit from behind A1 B1  B4, B5
left opposing vehicles hit from behind  B1  B5
right turning vehicles hit from behind A3 B2
standing water on roadway  G1
vehicles unable to stop safely (skidding)  G2
driver unaware of intersection D1, D2
nighttime conditions D1, D2
speed differentials of vehicles  A4, E4, E5
sudden stops A2, A3 A4
Safety Concern: High frequency of left-turn crashes attributed to:
left turn vehicles hit by opposing traffic A1, A3, C1 B1  B4, B5
nighttime conditions D1, D2
Safety Concern: High frequency of sideswipe crashes attributed to:
vehicles within intersection A1 B1
Safety Concern: High frequency of pedestrian/bicycle crashes:
on school routes or near generators of ped/bike traffic A6, B3 E2
vehicle/bicycle sideswipes on approaches  G1
with left turning vehicles A1, A3
Safety Concern: Address overall safety issues: empty cell
violation of traffic laws E1 E2
intersection near railroad crossing  G3
intersection near fire station  A5
excessive delay A7
disobedience of traffic signal A7
Note: Counter measures indicated on the table are possible treatments for individual crash problems. Implementation should be based on individual circumstances and studies.

CATEGORY A: REDUCE FREQUENCY AND SEVERITY OF INTERSECTION CONFLICTS THROUGH TRAFFIC CONTROL AND OPERATIONAL IMPROVEMENTS

Photograph if a horizontal signal head with a sign indicating left turning vehicles will receive a left turn arrow phase. A1 – Employ Multiphase Signal Operation (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of angle crashes involving left turning and opposing through vehicles. A properly timed protected left-turn phase can also help reduce rear-end and sideswipe crashes between leftturning vehicles and the through vehicles behind them. Time: Short. Effectiveness: Tried/Proven.

Photo of signalized intersection with one way only and right turn only signs mounted to the mast arm. A2 – Optimize Change Intervals (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes related to change interval lengths that are possibly too short. These crashes include angle crashes between vehicles continuing through the intersection after one phase has ended and the vehicles entering the intersection on the following phase. Rear-end crashes may also be a symptom of short change intervals.Time: Short. Effectiveness: Proven.

Photo of signalized intersection with one way only and right turn only signs mounted to the mast arm. A3 – Restrict or eliminate turning maneuvers (including right turns on red) (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes related to turning maneuvers. For right turn on red (RTOR), the target of this strategy is right-turning vehicles that are involved in rear-end or angle crashes with cross-street vehicles approaching from the left or vehicles turning left from the opposing approach, and crashes involving pedestrians. Time: Short. Effectiveness: Tried.

Photo of signalized intersection with one way only and right turn only signs mounted to the mast arm. A4 – Employ signal coordination (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes related to turning maneuvers. For right turn on red (RTOR), the target of this strategy is right-turning vehicles that are involved in rear-end or angle crashes with cross-street vehicles approaching from the left or vehicles turning left from the opposing approach, and crashes involving pedestrians. Time: Medium. Effectiveness: Proven.

Photo of a signal head and a preemption device mounted on a mast arm. A5 – Employ emergency vehicle preemption (HTML | PDF). WHERE TO USE – Signalized intersections where normal traffic operations impede emergency vehicles and where traffic conditions create a potential for conflicts between emergency and non-emergency vehicles. Time: Medium. Effectiveness: Proven.

Photo of a pedestrian countdown signal head. A6 – Improve operation of pedestrian and bicycle facilities at signalized intersections (HTML | PDF). WHERE TO USE – Signalized intersections with high frequencies of pedestrian and/or bicycle crashes. Also on routes serving schools or other generators of pedestrian and bicycle traffic. Time: Short. Effectiveness: Tried/Proven.

Photo of a roadway with a large sign that indicates the signal ahead is under study for removal. A7 – Remove unwarranted signal (HTML | PDF). WHERE TO USE – Signalized intersections where the traffic volumes and safety record do not warrant a traffic signal. Time: Short. Effectiveness: Proven.

CATEGORY B: REDUCE INTERSECTION CONFLICTS THROUGH GEOMETRIC IMPROVEMENTS


Photos showing left turn lane at a signalized intersection. B1 – Provide/improve left-turn channelization (HTML | PDF). WHERE TO USE – Signalized intersections where crashes related to left-turn movements are an issue. Time: Medium. Effectiveness: Tried/ Proven.

Photo of a right turn lane separated by a channelizing island that also serves as a pedestrian island. B2 – Provide/improve right-turn channelization (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of rear-end collisions resulting from conflicts between: (1) vehicles turning right and following vehicles; and (2) vehicles turning right and through vehicles coming from the left on the cross street. Time: Medium. Effectiveness: Proven.

Photo of a roadway containing a dedicated bike lane to the right of vehiclular traffic. B3 – Improve geometry of pedestrian and bicycle facilities (HTML | PDF). WHERE TO USE – Signalized intersections with high frequencies of pedestrian and/or bicycle crashes and on routes serving schools or other generators of pedestrian and bicycle traffic. Time: Short. Effectiveness: Tried/Proven.

Photo of an intersection where the through lane is aligned with the opposing left turning lane. B4 – Revise geometry of complex intersections (HTML | PDF). WHERE TO USE – Signalized intersections with high levels of crashes on a leg where other low-cost strategies have not been successful or are not considered appropriate. Time: Long. Effectiveness: Tried/Proven.

Photo of an intersection that uses a jughandle before the crossroad and a loop roadway beyond the crossroad to provide indirect left turn treatments. B5 – Construct special solutions (HTML | PDF). WHERE TO USE – Signalized intersections with high frequencies of crashes that are not reduced through other lower-cost solutions. Time: Long. Effectiveness: Tried.

CATEGORY C: IMPROVE SIGHT DISTANCE AT SIGNALIZED INTERSECTIONS

Photo of an intersection where the view of perpendicular oncoming traffic is blocked by overgrown shrubbery on the corner. C1 – Clear sight triangles (HTML | PDF). WHERE TO USE – Signalized intersections where there is a high frequency of crashes between vehicles turning right on red from one street and through vehicles on the other street or crashes involving left turning traffic where landscaped medians are present. Time: Short. Effectiveness: Tried.

Aerial photo of road with a Y-split that has been treated with a newly built road segment that connects the two branches of the Y and a signalized intersection at the connector. C2 – Redesign intersection approaches (HTML | PDF). WHERE TO USE – Signalized intersections with safety problems related to sight distance that cannot be addressed with less expensive methods. Time: Long. Effectiveness: Proven.

CATEGORY D: IMPROVE DRIVER AWARENESS OF INTERSECTIONS AND SIGNAL CONTROL

Photo showing a sign advising drivers to prepare to stop ahead when the attached warning lights are flashing. D1 – Improve visibility of intersections on approach(es) (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes attributed to drivers being unaware of the presence of the intersection. Time: Short. Effectiveness: Tried.

Two photos of intersections, one in which backplates have been placed around each signal head to improve visibility of the signal lights against the sun and the other showing an intersection where two side-by-side red light lenses are on each signal head instead of one. D2 – Improve visibility of signals and signs at intersections (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of right-angle and rear-end crashes occurring because drivers are unable to see traffic signals and signs sufficiently in advance to safely negotiate the intersection being approached. Time: Short. Effectiveness: Tried.

CATEGORY E: IMPROVE DRIVER COMPLIANCE WITH TRAFFIC CONTROL DEVICES

Collage of images including a screenshot of a web page, a brochure, and a photo of a device that shows both the posted speed limit and the actual speed of a vehicle as it approaches the device. E1 – Provide public information and education (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes related to drivers either being unaware of (or refusing to obey) traffic laws and regulations that impact traffic safety (especially red-light running, speeding, and not yielding to pedestrians). Time: Short. Effectiveness: Tried.

Photograph of a traffic signal with a red light mounted on top that can be seen from any angle when lit. E2 – Provide targeted conventional enforcement of traffic laws (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes related to drivers either being unaware of (or refusing to obey) traffic laws and regulations that impact traffic safety. Time: Short. Effectiveness: Tried.

Front and back photographs of a post-mounted box containing a lens and camera equipment. E3 – Implement automated enforcement of red-light running (cameras) (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of right-angle and rear-end crashes attributed to drivers who intentionally disobey red signal indications. Time: Medium. Effectiveness: Proven.

Photo of a vehicle on a roadway with two pole-mounted cameras on the side of the road. E4 – Implement automated enforcement of approach speeds (cameras) (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes attributed to drivers who intentionally disobey posted approach speed limits. Time: Medium. Effectiveness: Tried.

Photo of a rural roadway with a pole-mounted speed limit sign. E5 – Control speed on approaches (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes attributed to drivers who intentionally disobey posted approach speed limits. Time: Medium. Effectiveness: Experimental.

CATEGORY F: IMPROVE ACCESS MANAGEMENT NEAR SIGNALIZED INTERSECTIONS

Photo of a four-lane roadway in a business district in which traffic is prevented from turning by a physical barrier comprised of a series of flexible surface mounted delineator rods in the centerline. F1 – Restrict access to properties using driveway closures or turn restrictions (HTML | PDF). WHERE TO USE – Signalized intersections with high crash frequencies related to driveways adjacent to the intersection. Generally, driveways within 250 feet of the intersection are the greatest concern. Time: Short. Effectiveness: Tried.

Photo of an intersection in a business district in which a raised curb with delineator rods runs along the length of a left turn lane. F2 – Restrict cross-median access near intersections (HTML | PDF). WHERE TO USE – Approaches to signalized intersections with a high frequency of crashes involving drivers making turns across medians. Time: Short. Effectiveness: Tried.

CATEGORY G: IMPROVE SAFETY THROUGH OTHER INFRASTRUCTURE TREATMENTS

Two photos of drainage grates in the roadway at the curb, one in a bike lane and one at the junction of a raised curb and an at-grade curb. G1 – Improve drainage in intersection and on approaches (HTML | PDF). WHERE TO USE – Signalized intersections with a high frequency of crashes that are related to poor drainage. Such crashes involve vehicles that hydroplane and, hence, are not able to stop when required. Time: Medium. Effectiveness: Tried.

Photo of a an approach to a signalized intersection where the signal  immediately precedes an at-grade rail crossing. G2 – Provide skid resistance in intersection and on approaches (HTML | PDF). WHERE TO USE – Signalized intersection approaches where skidding is determined to be a problem, especially in wet conditions. Time: Medium. Effectiveness: Tried.

Photo of a an approach to a signalized intersection where the signal  immediately precedes an at-grade rail crossing. G3 – Coordinate closely spaced signals near at-grade railroad crossings (HTML | PDF). WHERE TO USE – Signalized intersections in close proximity to at-grade railroad crossings with a high frequency of crashes. This situation presents a significant potential for vehicletrain crashes, but vehicle-vehicle crashes could also occur if drivers try to speed through an intersection to avoid waiting in a queue near the railroad crossing. Time: Medium. Effectiveness: Tried.

Photo of an intersection where the signal hardware box is set well back from the roadway. G4 – Relocate signal hardware out of clear zone (HTML | PDF). WHERE TO USE – Signalized intersections where signal hardware is located within the clear zone or is a sight obstruction (particularly on high-speed approaches). Time: Short. Effectiveness: Tried.

Photo of an intersection in an urban area where signs prohibit parking on the approach to the intersection. G5 – Restrict or eliminate parking on intersection approaches (HTML | PDF). WHERE TO USE – Signalized intersections with permitted parking on the approaches that may present a safety hazard either by blocking sight distance or due to parking maneuvers. Time: Short. Effectiveness: Proven.

Stylized bar graph shows that, according to the National Highway Traffic Safety Administration FARS database, in 2006, 2,718 fatalities occurred at signalized intersections, 5,715 fatalities occurred at unsignalized intersections, and 364 fatalities occurred under other/unknown conditions.

Program Contact

Jeffrey Shaw

708-283-3524

What’s New

New Signalized Intersections: An Informational Guide

South Carolina Case Study: Systematic Intersection Improvements

Roundabout Outreach and Education Toolbox

Stop-Controlled Intersection Safety: Through Route Activated Warning Systems

Roundabouts: An Informational Guide, Second Edition (NCHRP Report 672)

Roundabouts Peer-to-Peer Assistance

How to drive a roundabout (WSDOT)

Modern Roundabouts: A Safer Choice

Highlights

FHWA's Intersection Resources Library CD-ROM

Roundabouts Technical Summary

Mini-Roundabouts Technical Summary

Access Management in the Vicinity of Intersections Technical Summary

Intersection Safety Case Studies

Intersection Safety Technologies

Presentation: Intersection Safety

Example Intersection Safety Implementation Plan

Intersection Safety Implementation Plan Workshop

Example Data Analysis Package and Straw Man Outline