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FHWA Home / Safety / HSIP / HRRR / Manual for Selecting Safety Improvements on High Risk Rural Roads

4. Selecting Safety Treatments (continued)

4.2 Intersections (Signalized)

4.3. Intersections (Unsignalized)

Intersection-specific safety treatments assist drivers in recognizing they are at or approaching an unsignalized intersection, provide storage for turning traffic,24 and give positive guidance to motorists through the intersection. Among others, improvements cited in this section include Railway-Highway Grade Crossing treatments.

Safety Treatment For more information, visit page Cost Frequency of Maintenance (years) Safety Benefit Benefit Cost Ratio25
Initial Implementation Ongoing Maintenance NCHRP 500 Performance Rating Crash Modification Factor (CMF) 4-Leg Intersection 3-Leg Intersection
Lower Volume* Higher Volume** Lower Volume* Higher Volume**
Relocate an Existing Stop Bar on Minor Approach 40 $     T          
Install Stop Ahead Pavement Markings 41 $     P 0.69        
Install Advanced Intersection Warning Signs 42 $     T          
Provide a Stop Bar on Minor-Road Approaches 43 $ - 5 P   337.7 1175.8 287.1 1484.1
Improve Sight Distance within Sight Triangle 44 $ $ 5 P 0.44-0.89 157.3 547.8 66.9 345.7
Provide Upcoming Road Names on Advanced Warning Signs 45 $     T 0.90-0.99        
Install Retroreflective Strips on Sign Posts 46 $     T          
Upgrade to Larger Stop Signs 47 $     P          
Double Use of Stop Signs 48 $     T          
Improve Sight Distance and Conspicuity at Railroad Grade Crossings 49 $     T          
Install a Splitter Island 50 $$     T          
Channelization of Major and Minor Roads (Physical or Painted) 51 $$     P          
Provide Intersection Lighting 52 $$ $ 1 P   23.1 80.6 10.5 54.2
Install Dynamic Advanced Intersection Warning System 53 $$     P 0.10-0.76        
Upgrade Existing Railroad Crossing Hardware and Warning Systems 54 $$-$$$     P 0.55        
Implement Lane Narrowing through Rumble Strips and Painted Median at Rural Stop-Controlled Approaches 55 $$-$$$     T 0.60-0.80        
Provide Flashing Beacons at Intersection Approaches 56 $$$ $ 2 P 0.85 16.3 56.8 6.8 35.8
Convert Minor-Road Stop Control to All-Way Stop Control 57 $$$ $ 10 P 0.30 77.2 268.8 32.8 169.7
Convert a Traditional Stop-Controlled Intersection into a J-Turn Intersection 58 $$$-$$$$ $ 10 P 0.0-0.9 46.4 161.4 n/a n/a
Use Raised Median to Restrict Turning Movements 59 $$$-$$$$     P          
Install Acceleration or Deceleration Lanes 60 $$$-$$$$                
Install Railroad Crossing Hardware and Warning Systems Where They Currently Do Not Exist 61 $$$-$$$$                
Convert a 4-Leg Intersection into Two 3-Leg Intersections (Offset T-Intersections) 62 $$$$                
Install Bypass Lane 63 $$$$ $$ 10 P   11.6 40.6 5.0 25.6
Modify Horizontal and/or Vertical Geometry 64 $$$$$     P          
Improve Horizontal Intersection Alignment or Skew 65 $$$$$ - - P   1.0 7.9 1.0 7.9
Install Traffic Signals 66 $$$$$ $$ 1 P 0.23-1.58 15.4 53.8 6.9 35.5
Install Right Turn Lane 67 $$$$$ $$ 10 P   16.0 55.9 6.8 35.3
Install Left Turn Lane 68 $$$$$ $$ 10 P   6.0 20.8 3.7 18.9
Install Offset (or Channelized) Left Turn Lane 69 $$$$$ $$ 10 P   6.0 20.8 3.7 18.9
Install a Roundabout (From Stop-Controlled) 70 $$$$$ $$ 10 P 0.54-1.11 4.8 16.8    
Remove or Separate an Existing Railroad Grade Crossing 71 $$$$$     P          

Cost:
$ = $0 to $5,000
$$ = $5,001 to $20,000
$$$ = $20,001 to $50,000
$$$$ = $50,001 to $100,000
$$$$$ = $100,001 and up

NCHRP 500 Performance rating26
P – Proven
T – Tried
E – Experimental
U – Unknown

*Lower Volume <1000 vpd
**Higher Volume = Between 1,001 and 8000 vpd


Relocate an Existing Stop Bar on Minor Approach

A minor approach may have an existing stop bar that is located where vehicles stopping at the bar have limited sight distance at the intersection. The stop bar may be relocated closer to the intersection at a point where the stopped vehicle would have better sight distance for approaching traffic.

Minor road approach featuring stop bar.

Where to Use: This treatment may be used at locations where existing sight distance may be obstructed or where sight distance may be significantly improved by moving the stop bar.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Relocate an Existing Stop Bar on Minor Approach $0 to $5,000 Tried

Top Recommended Resource:

1. FHWA. NCHRP Report 500 / Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, "Strategy E4. Provide a Stop Bar (or Provide a Wider Stop Bar) on Minor Road Approaches," July 2003. Available at: http://safety.fhwa.dot.gov/intersection/resources/intsafestratbro/ue4.cfm.

Install Stop Ahead Pavement Markings

Providing pavement markings with supplementary messages (such as Stop Ahead) can help alert drivers on the stop-controlled approach to the presence of an intersection.

Roadway with 'Stop Ahead' marked in advance of an intersection.

Where to Use: It is likely that Stop Ahead pavement markings will be most effective at locations with a high frequency of target collisions (i.e., right-angle and rear-end), particularly where driver awareness may be an issue.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating Crash Modification Factor (CMF)
IInstall Stop Ahead Pavement Markings $0 to $5,000 Proven 0.44-0.69

Top Recommended Resource:

1. FHWA, Techbrief: Safety Evaluation of STOP AHEAD Pavement Markings, March 2008. Available at: https://www.fhwa.dot.gov/publications/research/safety/08045/.

Install Advanced Intersection Warning Signs

Advanced intersection warning signs can help alert drivers to the presence of an intersection ahead. Signs can be placed with sufficient distance prior to the intersection to allow drivers to perceive and react. They can also be installed on both sides of the roadway to solicit greater awareness.

Diagram shows positioning of advanced warning signs on the approach to a cross street.

Where to Use: Advanced intersection warning signs are to be applied predominantly on single through lane, high-crash, stop-controlled State intersections in both rural and urban areas. They may also be applied on dual through lane, high-crash, stop-controlled intersections with lower traffic volumes (less than about 25,000 average annual daily traffic (AADT)) where the use of J-treatments is not appropriate and the frequency of acceptable gaps for entering traffic is such that long waiting and higher risk taking are present at the intersection.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Install Advanced Intersection Warning Signs $0 to $5,000 Proven

Top Recommended Resources:

1. FHWA, Example Intersection Safety Implementation Plan, 2009.

2. FHWA, Stop-Controlled Intersection Safety: Through Route Activated Warning Systems, February 2011.

Provide a Stop Bar on Minor-Road Approaches

Providing visible stop bars on the minor road approach to an unsignalized intersection can help direct the attention of drivers to the presence of the intersection.

A visible stop bar on a minor road approach to an unsignalized intersection.

Where to Use: Minor road approaches where conditions allow the stop bar to be seen by an approaching driver at a significant distance from the intersection. Locations should be identified by patterns of crashes related to lack of driver recognition of the intersection.

Provide a Stop Bar on Minor-Road Approaches
- Initial Investment: $1,000 (4ST), $500 (3ST)
- Cost of Maintenance: $0
- Frequency of Maintenance: 5 years (4 applications)
Benefit-Cost Ratio NCHRP 500 Performance Rating
Lower Volume 4-Way Intersections 337.7 Proven
Higher Volume 4-Way Intersections 1175.8 Proven
Lower Volume 3-Way Intersections 287.1 Proven
Higher Volume 3-Way Intersections 1484.1 Proven

Top Recommended Resource:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

Improve Sight Distance within Sight Triangle

By removing sight distance restrictions (e.g., vegetation, parked vehicles, signs, buildings) from the sight triangles at stop or yield-controlled intersection approaches, drivers will be able see approaching vehicles on the main line without obstruction and therefore make better decisions about entering the intersection safely.

Artist's rendering of a sight triangle on the approach to an unsignalized intersection. The presence of vegetation interrupts and blocks the driver's view at some points on the triangle.

Where to Use: This treatment may be used at 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.

Improve Sight Distance within Sight Triangle
- Initial Investment: $4,500
- Cost of Maintenance: $1,000
- Frequency of Maintenance: 5 years
Benefit-Cost Ratio NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Lower Volume 4-Way Intersections 157.3 Proven 0.44-0.89
Higher Volume 4-Way Intersections 547.8 Proven 0.44-0.89
Lower Volume 3-Way Intersections 66.9 Proven 0.44-0.89
Higher Volume 3-Way Intersections 345.7 Proven 0.44-0.89

Top Recommended Resource:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

Provide Upcoming Road Names on Advanced Warning Signs

At locations where Intersection Ahead warning signs are used, it is recommended that street name plaques be placed underneath the upcoming street sign. These street name plaques provide the driver with additional information about the street so he or she can make an early decision regarding potential turning movements.

Examples of signs identifying the names of upcoming cross streets.

Where to Use: This treatment may be used at locations where crashes could potentially be reduced by providing advanced turn information.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Provide Upcoming Road Names on Advanced Warning Signs $0 to $5,000 Tried 0.90-0.99

Top Recommended Resource:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

Install Retroreflective Strips on Sign Posts

The use of retroreflective strips on sign posts may be beneficial when there is a need to draw additional attention to the signs, especially at night. Reflective strips may be added to Stop signs, curve or intersection warning signs, regulatory or guidance signs, etc.

A stop sign with retroreflective strips on the sign post.

Where to Use: The MUTCD provides the following guidance for the use of reflective strips on sign posts: "The material must be at least 2 inches wide and must be placed the full length of the post, from the sign to within 2 feet above the horizontal surface into which the sign is fixed. In addition, the color of the material must match the background color of the sign except that the color of the strip for Yield and Do Not Enter signs must be red."

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Install Retroreflective Strips on Sign Posts $0 to $5,000 Tried

Top Recommended Resource:

1. FHWA, "Intersection Safety Implementation Plan Workshop," presentation, July 2009. Available at: http://safety.fhwa.dot.gov/intersection/other_topics/fhwasa10010/fhwasa10010.pdf.

Upgrade to Larger Stop Signs

A high number of crashes relate to the driver's inability or failure to see the Stop sign at stop-controlled intersections. To improve recognition of the signs, larger Stop signs can be installed. Sizes can range from 30 inches, to 36 inches, to 48 inches and larger, if needed.

Larger sized stop sign at an unsignalized intersection.

Where to Use: While roadway classification and speed can help determine proper Stop sign size, larger sizes may be used when crash types indicate that Stop sign visibility may be an issue.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Upgrade to Larger Stop Signs $0 to $5,000 Proven

Top Recommended Resource:

1. FHWA, Stop Sign-Controlled Intersections: Enhanced Signs and Markings–A Winston-Salem Success Story, November 2009. Available at: http://safety.fhwa.dot.gov/intersection/resources/casestudies/fhwasa09010/.

Double Use of Stop Signs

Two Stop signs (mounted left and right) can be used to call greater attention to the need for motorists to stop at an intersection. The first Stop sign is installed at the traditional right side location; a second is recommended in the median (if available) of the approach. To accommodate this left-mounted Stop sign, a small mountable curb is suggested. This curb and associated pavement markings provide the motorist with additional information that he or she is entering an intersection.

Stop signs to the right and left of an intersection on a cross-street approach.

Where to Use: This treatment may be used at locations where crashes indicate that motorists do not obey existing Stop signs and additional intersection conspicuity is needed.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Double Use of Stop Signs $0 to $5,000 Tried

Top Recommended Resources:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

2. FHWA, Stop Sign-Controlled Intersections: Enhanced Signs and Markings – A Winston-Salem Success Story, November 2009. Available at: http://safety.fhwa.dot.gov/intersection/resources/casestudies/fhwasa09010/.

Improve Sight Distance and Conspicuity at Railroad Grade Crossings

Where passive warning devices are used at railroad crossings, improvements in vertical alignment or through removing vegetation and other obstructions can help to provide increased sight distance. Conspicuity of the intersection may be helped by providing brighter sign sheeting or upgrading to larger signs.

At-grade railroad crossing.

Where to Use: This treatment is appropriate for use at all railroad grade crossings.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Improve Sight Distance and Conspicuity at Railroad Grade Crossings $0 to $5,000 Tried

Top Recommended Resource:

1. FHWA, Railroad-Highway Grade Crossing Handbook, Revised Second Edition, August 2007. Available at: http://safety.fhwa.dot.gov/xings/com_roaduser/07010/.

Install a Splitter Island

A splitter island separates traffic moving in opposite directions of travel. A splitter island that is installed on the minor approach creates a physical separation between other vehicles that are turning onto the minor road. In addition, the installation of a splitter island allows for a second Stop sign to be mounted in the median to make the intersection more conspicuous.

A splitter island separating opposing direction traffic on the cross-street approach to an intersection.

Where to Use: Splitter islands should be applied to minor road approaches of 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.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Install a Splitter Island $0 to $5,000 Tried

Top Recommended Resources:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

Channelization of Major and Minor Roads (Physical or Painted)

The installation of channelizing separator islands at stop-controlled intersection approaches can accommodate redundancy of the Stop sign and increase driver compliance with the Stop sign.

A channelizing separator island at a stop-controlled intersection approach.

Where to Use: This practice has greater potential for effectiveness on intersections of high-speed roadways; however, they can also be applied to intersections with lower posted speed limits.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Channelization of Major and Minor Roads (Physical or Painted) $5,001 to $20,000 Proven

Top Recommended Resource:

1. FHWA, Summary Report: Two Low-Cost Safety Concepts for Two-Way STOP-Controlled, Rural Intersections on High-Speed Two-Lane, Two-Way Roadways, December 2008. Available at: https://www.fhwa.dot.gov/publications/research/safety/08063/.

Provide Intersection Lighting

Many intersection crashes during late-night and early-morning hours occur due to drivers being unable to see conflicting traffic, other road users, or–specifically in the case of unsignalized intersections–the presence of the intersection itself. At night in rural areas, the only source of lighting for roadways is often provided by vehicle headlights. Roadway lighting allows for greater visibility of the intersection, making signs and markings more visible and helping drivers determine a safe path through the intersection.

A pole-mounted light illuminates an intersection at night.

Where to Use: Lighting should be provided at signalized or unsignalized intersections, particularly those with a high instance of dark crashes. 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.

Provide Intersection Lighting
- Initial Investment: $20,000
- Cost of Maintenance: $500
- Frequency of Maintenance: 1 year
Benefit-Cost Ratio NCHRP 500 Performance Rating
Lower Volume 4-Way Intersections 23.1 Proven
Higher Volume 4-Way Intersections 80.6 Proven
Lower Volume 3-Way Intersections 10.5 Proven
Higher Volume 3-Way Intersections 54.2 Proven

Top Recommended Resources:

1. FHWA. NCHRP Report 500 / Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, "Strategy E2. Improve Visibility of the Intersection by Providing Lighting," July 2003. Available at: http://safety.fhwa.dot.gov/intersection/resources/intsafestratbro/ue2.cfm.

2. Minnesota DOT, Safety Impacts of Street Lighting at Isolated Rural Intersections – Part II, September 2006. Available at: http://www.intrans.iastate.edu/reports/rural_lighting_FINAL.pdf.

Install Dynamic Advanced Intersection Warning System

Infrastructure-based Intelligent Transportation System (ITS) technologies can be used to significantly improve the safety at stop-controlled intersections. These systems provide enhanced safety warning information for approaching drivers compared to passive warning systems. A dynamic advanced intersection warning system can provide:

Dynamic warning sign with flashers that activate to warn approaching through traffic that there is a vehicle on a cross road stop approach that may enter the intersection.

Where to Use: This treatment may be provided at intersections that experience severe intersection-related crashes due to speed, low visibility, or insufficient gaps.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Install Dynamic Advanced Intersection Warning System $5,001 to $20,000 Proven 0.10-0.76

Top Recommended Resource:

1. FHWA, Stop-Controlled Intersection Safety: Through Route Activated Warning Systems, February 2011. Available at: http://safety.fhwa.dot.gov/intersection/resources/fhwasa11015/traws.pdf.

Upgrade Existing Railroad Crossing Hardware and Warning Systems

The installation of enhanced railroad crossing hardware and warning systems not only notifies motorists as to the presence of an approaching train but can limit their ability to proceed through the intersection through the use of gates and other devices.

An at-grade rail crossing with a train traveling through.

Where to Use: This treatment is applicable where additional notification and/or the ability to limit drivers from proceeding through the crossing is needed.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Upgrade Existing Railroad Crossing Hardware and Warning Systems $5,001 to $50,000 Proven 0.55

Top Recommended Resource:

1. FHWA, Railroad-Highway Grade Crossing Handbook, Revised Second Edition, August 2007. Available at: http://safety.fhwa.dot.gov/xings/com_roaduser/07010/.

Implement Lane Narrowing through Rumble Strips and Painted Median at Rural Stop-Controlled Approaches

Lane narrowing features the introduction of rumble strips on the outside shoulders and in a painted yellow median island on the major road approaches. The objective of lane narrowing is to induce drivers on major roads to reduce approach speeds at intersections by effectively reducing the lane width.

Roadway with rumble strips on the outside shoulders and in a painted yellow median island

Where to Use: This practice has greater potential for effectiveness for intersections on high-speed roadways. However, the treatment can also be applied to intersections with lower posted speed limits.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Implement Lane Narrowing through Rumble Strips and Painted Median at Rural Stop-Controlled Approaches $5,001 to $50,000 Tried 0.60-0.80

Top Recommended Resource:

1. FHWA, Railroad-Highway Grade Crossing Handbook, Revised Second Edition, August 2007. Available at: http://safety.fhwa.dot.gov/xings/com_roaduser/07010/.

Provide Flashing Beacons at Intersection Approaches

Flashing beacons provide a visible signal indicating the presence of an intersection and can be very effective in rural areas where there may be long stretches between intersections. They may also improve safety at locations where nighttime visibility of intersections is an issue.

A stop sign with a flashing beacon mounted above it.

Where to Use: Flashing beacons can be installed at 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. The beacons can be installed either atop Stop signs or Advance Intersection Warning Signs, where applicable.

Provide Flashing Beacons at Intersection
Approaches
- Initial Investment: $25,000
- Cost of Maintenance: $1,000
- Frequency of Maintenance: 2 years
Benefit-Cost Ratio NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Lower Volume 4-Way Intersections 16.3 Proven 0.85
Higher Volume 4-Way Intersections 56.8 Proven 0.85
Lower Volume 3-Way Intersections 6.8 Proven 0.85
Higher Volume 3-Way Intersections 35.8 Proven 0.85

Top Recommended Resource:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, "Chapter 4. Countermeasures," January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/ch4.cfm.

Convert Minor Road Stop Control to All-Way Stop Control

At locations where there is a pattern of high-severity frontal impact crashes, all-way stop control can be implemented quickly by installing Stop signs on the unrestricted approach. It is important to ensure adequate sight distance for all stop conditions and to consult the MUTCD for proper installation guidelines.

A stop sign with a "4-Way" plaque below mounted below it.

Where to Use: This treatment can be installed at locations where there is a pattern of high severity frontal impact crashes.

Convert Minor Road Stop Control to All-Way Stop
Control
- Initial Investment: $30,000
- Cost of Maintenance: $5,000
- Frequency of Maintenance: 10 years
Benefit-Cost Ratio NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Lower Volume 4-Way Intersections 77.2 Proven 0.30
Higher Volume 4-Way Intersections 268.8 Proven 0.30
Lower Volume 3-Way Intersections 32.8 Proven 0.30
Higher Volume 3-Way Intersections 169.7 Proven 0.30

Top Recommended Resource:

1. FHWA. NCHRP Report 500 / Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, "Strategy F2. Provide All-Way Stop Control at Appropriate Intersections," July 2003. Available at: http://safety.fhwa.dot.gov/intersection/resources/intsafestratbro/uf2.cfm.

Convert a Traditional Stop-Controlled Intersection into a J-Turn Intersection

The J-turn intersection is characterized by the prohibition of left turn and through movements from side street approaches as permitted in conventional designs. The J-turn intersection accommodates these movements by requiring drivers to turn right onto the main road and then make a U-turn maneuver at a one-way median opening 400 to 1,000 feet after the intersection. Left turns from the main road approaches are executed in a manner similar to left turns at conventional intersections and are unchanged in this design. Left turn movements from the major road could also be removed at primarily rural unsignalized J-turn designs.

Aerial photo of a J-Turn road configuration.

Where to Use: J-turn intersections are typically implemented as part of a corridor treatment; however, they can be used at isolated intersections. Unsignalized J-turn intersections preserve corridor capacity and can be installed without the adverse effects of signal control. Scenarios where J-turn intersections are most applicable include the following:

For intersections with very high left turn and through volumes from the side road approaches, the J-turn intersection design is not the optimum choice.

Convert a Traditional Stop-Controlled Intersection into a J-Turn Intersection
- Initial Investment: $50,000-$100,000
- Cost of Maintenance: $5,000
- Frequency of Maintenance: 10 years
Benefit-Cost Ratio NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Lower Volume 4-Way Intersections 46.1 Proven 0.0-0.91
Higher Volume 4-Way Intersections 161.4 Proven 0.0-0.91
Lower Volume 3-Way Intersections n/a Proven 0.0-0.91
Higher Volume 3-Way Intersections n/a Proven 0.0-0.91

Top Recommended Resource:

1. FHWA, Restricted Crossing U-Turn Intersection, October 2009. Available at:
https://www.fhwa.dot.gov/publications/research/safety/09059/09059.pdf.

Use Raised Median to Restrict Turning Movements

Raised medians can be helpful in limiting access and restricting turning movements within the functional limits of intersections, thereby reducing conflicts between through traffic and turning vehicles.

A raised median separates opposing directional traffic.

Where to Use: This treatment may be used at locations where access to streets, businesses, homes, and other properties falls within the intersection functional area.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Use Raised Median to Restrict Turning Movements $20,001 to $100,000 Proven

Top Recommended Resource:

1. FHWA, Signalized Intersections Informational Guide, July 2013. Available at: http://safety.fhwa.dot.gov/intersection/conventional/signalized/fhwasa13027/.

Install Acceleration or Deceleration Lanes

Drivers turning onto an uncongested highway generally accelerate until they approach the desired open-road speed. When the entering traffic accelerates within the traveled way, it has the potential to disrupt the flow of through traffic. To minimize this operational problem due to right or left turning traffic at divided highway intersections, acceleration lanes may be used.

An acceleration lane is an auxiliary or speed-change lane that allows vehicles to accelerate to highway speeds before entering the through traffic lanes of a highway. Acceleration lanes should be of sufficient length to permit adjustments in speeds of both through and entering vehicles so that the driver of the entering vehicle can maneuver into that gap before reaching the end of the acceleration lane. Additionally, the purpose of a parallel deceleration lane is to provide drivers exiting or turning from the road with an opportunity to slow down to a more reasonable speed prior to turning.

An exceleration lane allows right-turning traffic to merge into the through lanes.

Where to Use: This treatment may be used at unsignalized intersections on divided highways that experience a high proportion of rear-end crashes related to the speed differential caused by vehicles turning left or right onto or from the highway. They may also be used where intersection sight distance is inadequate or where there are high volumes of trucks or recreational vehicles entering or exiting the divided highway. Acceleration or deceleration lanes can be added as median acceleration or deceleration lanes–as installed at several locations in Missouri—or as lanes next to the shoulder for vehicles entering or exiting the roadway on the right side—as installed in Kentucky.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Install Acceleration or Deceleration Lanes $20,001 to $100,000 Proven

Top Recommended Resources:

1. FHWA, NCHRP Report 500 / Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, "Strategy B9. Provide Right-Turn Acceleration Lanes at Intersections," 2003. Available at: http://safety.fhwa.dot.gov/intersection/resources/intsafestratbro/ub9.cfm

2. FHWA, NCHRP Report 500 / Volume 5: A Guide for Addressing Unsignalized Intersection Collisions, "Strategy B5. Provide Left-Turn Acceleration Lanes at Intersections," 2003. Available at: http://safety.fhwa.dot.gov/intersection/resources/intsafestratbro/ub9.cfm

Install Railroad Crossing Hardware and Warning Systems Where They Currently Do Not Exist

By installing railroad crossing hardware and warning devices, motorists are notified as to the presence of an approaching train and can make an informed decision whether to cross.

The approach to an at-grade rail crossing featuring gates, bells and flashers.

Where to Use: This treatment may be applied where railroad crossings exist with no form of warning device.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Install Railroad Crossing Hardware and Warning Systems Where They Currently Do Not Exist $20,001 to $100,000 Proven 0.75

Top Recommended Resource:

1. FHWA, Railroad-Highway Grade Crossing Handbook, Revised Second Edition, August 2007. Available at: http://safety.fhwa.dot.gov/xings/com_roaduser/07010/.

Convert a 4-Leg Intersection into Two 3-Leg Intersections (Offset T-Intersections)

For some 4-leg intersections with very low through volumes on the cross street, one method of improving safety may be to convert the intersection to two T-intersections. This conversion can be accomplished by realigning the two cross-street approaches an appreciable distance along the major road, thus creating separate intersections that operate relatively independently of one another.

Where to Use: This improvement may be applicable to 4-leg intersections with very low through volumes on the cross street, yet with a relatively high number of unusually severe collisions.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Convert a 4-Leg Intersection into Two 3-Leg Intersections (Offset T-Intersections) $50,001 to $100,000 Proven 0.70

Install Bypass Lane

Installation of this treatment is accomplished by adding bypass lanes using the shoulder at intersections. The bypass lanes are intended for vehicles to continue through the intersection without having to stop for traffic making left turns.

A two-lane road in which one travel lane that has been widened into two for a limited distance to allow slower vehicles to move over, allowing others to pass.

Where to Use: Bypass lanes should be used at 3-leg intersections on two-lane highways with moderate through and turning volumes, especially intersections that have rear-end collisions involving vehicles waiting to turn left from the mainline.

Install Bypass Lane
- Initial Investment: $75,000
- Cost of Maintenance: $20,000
- Frequency of Maintenance: 10 years
Benefit-Cost Ratio NCHRP 500 Performance Rating
Lower Volume 4-Way Intersections 11.6 Proven
Higher Volume 4-Way Intersections 40.6 Proven
Lower Volume 3-Way Intersections 5.0 Proven
Higher Volume 3-Way Intersections 25.6 Proven

Top Recommended Resource:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

Modify Horizontal and/or Vertical Geometry

Although changing alignment is a high-cost treatment, in some cases sight distance is restricted by horizontal and vertical curvature. Straightening a roadway will increase sight distance and allow for better visibility of other vehicles and the intersection itself.

Diagram showing how the steep alignment of a side street on the stop approach has been modified (flattened) to increase the sight distance to a T-intersection.

Where to Use: This treatment may be used at 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.

Top Recommended Resource:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

Improve Horizontal Intersection Alignment or Skew

Reducing or eliminating the skew at intersection approaches helps address problems like vehicle alignment, long exposure in the intersection, and potential driver confusion. Intersection skew treatments include pavement markings, channelizing islands, and realignment.

A splitter island separates diverging traffic on a y-shaped roadway.

Where to Use: This treatment may be used at unsignalized intersections with a high frequency of crashes resulting from insufficient intersection sight distance and awkward sight lines at a skewed intersection.

Improve Horizontal Intersection Alignment or Skew
- Initial Investment: $300,000
- Cost of Maintenance: n/a
- Frequency of Maintenance: n/a
Benefit-Cost Ratio NCHRP 500 Performance Rating
Lower Volume Optimal Conditions 1.0 Proven
Higher Volume Optimal Conditions 7.96 Proven

Top Recommended Resource:

1. FHWA, Intersection Safety: A Manual for Local Rural Road Owners, January 2011. Available at: http://safety.fhwa.dot.gov/local_rural/training/fhwasa1108/fhwasa1108.pdf.

Install Traffic Signals

Traffic signals help to assign right-of-way to traffic movements and have been shown to reduce the severity of total collisions experienced at intersections. The MUTCD lists eight warrants for the placement of traffic signals, which should be reviewed as installation of this treatment is considered. The safety benefit of signalizing an unsignalized intersection is a function of the crash history by crash type, the traffic entering the intersection on the major and minor approaches, and whether the intersection is a 3-leg T-intersection or a conventional 4-leg intersection.

Traffic signal at a rural intersection.

Where to Use: Traffic signals can be installed at intersections that experience a high frequency of right-angle collisions with adequate sight distance to that intersection from all approaches. Signalization may be particularly effective where the ratio of right-angle to rear-end crashes is high.

Install Traffic Signals
- Initial Investment: $150,000
- Cost of Maintenance: $8,000
- Frequency of Maintenance: 1 year
Benefit-Cost Ratio NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Lower Volume 4-Way Intersections 15.4 Proven 0.23-1.58
Higher Volume 4-Way Intersections 53.8 Proven 0.23-1.58
Lower Volume 3-Way Intersections 6.9 Proven 0.23-1.58
Higher Volume 3-Way Intersections 35.5 Proven 0.23-1.58

Top Recommended Resource:

1. AASHTO, NCHRP Report 617: Accident Modification Factors for Traffic Engineering and ITS Improvements, July 2008. Available at: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_617.pdf.

Install Right Turn Lane

Providing a right turn lane at an intersection can reduce rear-end crashes by allowing vehicles to proceed through the intersection without having to stop or slow down for vehicles making a right turn. Assuming turn lanes are of adequate length, vehicles will not be stopped in the travel lanes; this allows for through traffic to continue without stopping for vehicles turning at an intersection.

A right turn lane on a rural four-lane road.

Where to Use: Right turn lanes should be constructed at 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.

Install Right Turn Lane
- Initial Investment: $400,000
- Cost of Maintenance: $20,000
- Frequency of Maintenance: 10 years
Benefit-Cost Ratio NCHRP 500 Performance Rating
Lower Volume 4-Way Intersections 16.0 Proven
Higher Volume 4-Way Intersections 55.9 Proven
Lower Volume 3-Way Intersections 6.8 Proven
Higher Volume 3-Way Intersections 35.3 Proven

Top Recommended Resources:

1. FHWA, Techbrief: Safety Effectiveness of Intersection Left- and Right-Turn Lanes, 2002. Available at: https://www.fhwa.dot.gov/publications/research/safety/02103/02103techbrief.pdf

2. FHWA, Safety Effectiveness of Intersection Left- and Right-Turn Lanes, July 2002. Available at: https://www.fhwa.dot.gov/publications/research/safety/02089/02089.pdf.

Install Left Turn Lane

Left turn lanes are auxiliary lanes for storage or to accommodate the decreasing speed of left turning vehicles as they approach the intersection speed change of left turning vehicles. Installing left turn lanes at an intersection can reduce rear-end crashes by allowing vehicles to proceed through the intersection without having to stop or slow down for vehicles waiting to make a left turn.

A left turn lane on a two-lane rural road.

Where to Use: The AASHTO Green Book recommends that left turning traffic be removed from the through lanes whenever practical, and that left turn lanes should be provided at street intersections along major arterials and collector roads wherever left turns are permitted. Consideration of left turn lanes has traditionally been based on such factors as the number of through lanes, speeds, left turn volumes, opposing through volumes, and/or left turning crashes.

Intersections with a high frequency of crashes resulting from the conflicts between (1) vehicles turning left and following vehicles, and (2) vehicles turning left and opposing through vehicles are also candidates for the installation of left turn lanes.

Practitioners should consider installing left turn lanes for the major road approaches to improve safety at 3- and 4-leg intersections with two-way stop control on the minor road at locations where significant turning volumes exist or where there is a history of turn-related crashes.

Install Left Turn Lane
- Initial Investment: $400,000
- Cost of Maintenance: $20,000
- Frequency of Maintenance: 10 years
Benefit-Cost Ratio NCHRP 500 Performance Rating
Lower Volume 4-Way Intersections 6.0 Proven
Higher Volume 4-Way Intersections 20.8 Proven
Lower Volume 3-Way Intersections 3.7 Proven
Higher Volume 3-Way Intersections 18.9 Proven

Top Recommended Resource:

1. AASHTO, NCHRP Report 617: Accident Modification Factors for Traffic Engineering and ITS Improvements, July 2008. Available at: http://onlinepubs.trb.org/onlinepubs/nchrp/nchrp_rpt_617.pdf.

Install Offset (or Channelized) Left Turn Lane

Offset left turn lanes provide the left turning motorist a line of sight to opposing through vehicles. Instead of attempting to look around opposing left turning vehicles, the motorist can clearly see oncoming traffic.

A channelized left-turn lane on a four-lane rural roadway.

Where to Use: Offset left turn lanes should be used at unsignalized 4-leg intersections with a high frequency of crashes between vehicles turning left and opposing through vehicles. This treatment can be applied at intersections on divided highways with medians wide enough to provide the appropriate positive offset, and also on approaches without medians if sufficient width exists.

Install Left Turn Lane
- Initial Investment: $400,000
- Cost of Maintenance: $20,000
- Frequency of Maintenance: 10 years
Benefit-Cost Ratio NCHRP 500 Performance Rating
Lower Volume 4-Way Intersections 6.0 Proven
Higher Volume 4-Way Intersections 20.8 Proven
Lower Volume 3-Way Intersections 3.7 Proven
Higher Volume 3-Way Intersections 18.9 Proven

Top Recommended Resource:

1. FHWA, Signalized Intersections Informational Guide, July 2013. Available at: http://safety.fhwa.dot.gov/intersection/conventional/signalized/fhwasa13027/.

Install a Roundabout (From Stop-Controlled)

The modern roundabout is a type of circular intersection defined by the basic operational principle that entering traffic yields to vehicles on the circulatory roadway. Key design principles achieve deflection of entering traffic by channelization at the entrance and deflection around a center island. Roundabout intersections eliminate a number of vehicle conflict points typically associated with traditional intersections. A 4-leg, single-lane roundabout has 75 percent fewer vehicle conflict points than a traditional stop-controlled intersection. Roundabouts also enhance safety by reducing vehicle speeds both in and through the intersection and by changing the crash type from angle to sideswipe, which typically results in less severe crashes.

A single-lane roundabout.

Where to Use: Roundabouts are the preferred safety alternative for a wide range of intersections. Although they may not be appropriate in all circumstances, they may be considered as an alternative for all proposed new intersections on federally funded highway projects. Roundabouts should also be considered for all existing intersections that have been identified as needing major safety or operational improvements. This would include freeway interchange ramp terminals and rural intersections.

Install a Roundabout (From Stop-Controlled)
- Initial Investment: $400,000
- Cost of Maintenance: $40,000
- Frequency of Maintenance: 10 years
Benefit-Cost Ratio NCHRP 500 Performance Rating Crash Modification Factor (CMF)
Lower Volume 4-Way Intersections 4.8 Proven 0.54-1.11
Higher Volume 4-Way Intersections 16.8 Proven 0.54-1.11
Lower Volume 3-Way Intersections n/a Proven 0.54-1.11
Higher Volume 3-Way Intersections n/a Proven 0.54-1.11

Top Recommended Resources:

1. FHWA, "Guidance Memorandum on Consideration and Implementation of Proven Safety Countermeasures," July 2010. Available at: http://safety.fhwa.dot.gov/policy/memo071008/.

2. FHWA, Intersection Safety Case Study: Minnesota Roundabout – A Scott County Success Story, February 2010. Available at: http://safety.fhwa.dot.gov/intersection/resources/casestudies/fhwasa09013/.

Remove or Separate an Existing Railroad Grade Crossing

Conflicts between road users and trains can be reduced by completely eliminating a crossing or separating it from vehicular traffic. This will likely divert traffic to another grade crossing, whether it is a grade-separated structure or another at-grade intersection.

A grade-separated rail crossing above a roadway.

Where to Use: This treatment may be applicable where a high frequency of severe vehicle-rail crashes occur and at locations where more suitable alternative crossings are available.

Safety Treatment Initial Implementation Cost NCHRP 500 Performance Rating
Remove or Separate an Existing Railroad Grade Crossing $100,001 and up Proven

Top Recommended Resource:

1. FHWA, Railroad-Highway Grade Crossing Handbook - Revised Second Edition, 2007. Available at: http://safety.fhwa.dot.gov/xings/com_roaduser/07010/




24 Turn lane storage is the length of turn lane provided based on anticipated traffic needs. [ Return to note 24. ]

25 As discussed in Section 1.2, a BCR is only shown where data were available to calculate the ratio. Where data were unavailable, the BCR has been left blank. [ Return to note 25. ]

26 As stated in NCHRP Series 500 Reports (http://safety.transportation.org/guides.aspx). Proven: The safety effect for other similar applications has shown a proven benefit. Tried: The treatment has indications that it can be expected to reduce crashes, but has some conflicting reports as to its associated safety effects or has been deployed and observed to be effective. Experimental: New treatments that still need to be tested and for which the safety effect is unknown. Unknown: Not enough is known about an associated safety performance. [ Return to note 26. ]

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