U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
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The major severe crash type at signalized intersections is a right-angle crash where one vehicle violates the red signal. Rear-end crashes occur with a much higher frequency but are much less severe than angle crashes. Two other concerns at signalized intersections are crashes involving left turn-opposing flow crashes and pedestrian crashes.
The low-cost countermeasures for signalized intersections are identified below. Countermeasures have been classified as basic or supplemental. Basic countermeasures are those that are usually very low in unit cost and effective in terms of reducing future crash potential. Supplemental countermeasures are targeted to intersections with specific crash concerns.
The basic set of countermeasures should be considered as a package of minor improvements consisting of all of the above countermeasures.
In addition to the basic package of countermeasures, additional individual countermeasures can be considered based upon higher frequencies of crashes beyond the crash threshold for basic countermeasures or at intersections that have specific crash types that the countermeasure can address.
It is assumed that the existing traffic signals at the intersection are MUTCD compliant and consist of at least dual signal heads on each approach. The estimated crash reduction factor for the combined basic countermeasures is a 30 percent reduction in all crashes. This estimate was developed by an expert intersection safety panel using past effectiveness research findings for individual countermeasures combined with engineering judgment. Crash reduction factors for supplemental enhancements for special conditions have been taken from the FHWA Toolbox of Countermeasures and Their Potential Effectiveness to Make Intersections Safer and other FHWA research publications and are indicated in Table 3.
|Countermeasure||Crash Reduction Factor||Typical Urban Crash Threshold||Typical Rural Crash Threshold||Additional Implementation Factors||Typical Implementation Cost Range per Intersection|
|Basic set of sign and marking improvements||30%||20 crashes in 5 years||10 crashes< in 5 years||None||$5,000 to $30,000|
|Change of permitted and protected left-turn phase to protected-only||41-48% of left turn crashes||5 left turn movement crashes; 3 or more opposing through lanes; minimal turning gaps available||5 left turn movement crashes; 3 or more opposing through lanes; minimal turning gaps available||None||$5,000 to $10,000|
|Advance cross street name signs for highspeed approaches on arterial highways||Unknown||20 crashes in 5 years||10 crashes in 5 years||High-speed approaches on four or more lane arterial highways||$1,000 to $5,000|
|Advance left and right “Signal Ahead” warning signs for isolated traffic signals||22%||20 crashes in 5 years||10 crashes in 5 years||Isolated traffic signal with one or more miles between signals; or traffic signals that are not readily visible due to highway alignment or obstructions||$1,000|
|Supplemental signal face per approach||28%||20 crashes in 5 years||10 crashes in 5 years||Signal faces obstructed by horizontal alignment; or exceptionally wide intersections (>100 ft) where a near side signal is needed||$5,000 to $15,000|
|Advance detection control systems||40% (injuries)||5 angle rashes in 5 years||5 angle crashes in 5 years||Isolated high-speed (45mph or greater) signalized intersections||$15,000|
|Signal coordination||32%||20 crashes in 5 years per intersection||10 crashes in 5 years per intersection||Arterials with closely spaced (about 1/2 mile maximum) signals||$5,000 to $50,000|
|Pedestrian countdown signals||25% (pedestrian crashes)||2 pedestrian crashes in 5 years||2 pedestrian crashes in 5 years||None||$5,000 to $15,000|
|Separate Pedestrian Phasing||34% pedestrian crashes)||2 pedestrian crashes in 5 years involving a turning vehicle||2 pedestrian crashes in 5 years involving a turning vehicle||None||$5,000 to $15,000|
|Pedestrian Ladder or cross-hatched crosswalk and advanced pedestrian warning signs||15% (pedestrian crashes) for signs Unknown for crosswalk||2 pedestrian crashes in 5 years||2 pedestrian crashes in 5 years||None||$1,000 to $3,000|
The typical crash threshold levels in Table 3 may be refined to reflect the following: entering traffic volumes (low-volume intersections may have a lower threshold); and/or differences in severity rates (e.g., fatalities per 100 crashes) between urban and rural signalized intersections. Further information on adjusting thresholds may be found in the "Systematic Approach" section of this document.
The basic set of signal and signing countermeasures should be the primary improvement considered at signalized intersections with a high frequency of crashes.
Additional supplemental countermeasures beyond the basic signal and sign enhancements should be considered at those intersections which either have much higher levels of crashes beyond the basic signal and sign improvement crash thresholds or have other intersection concerns identified in Table 3 that may be addressed by a given countermeasure.
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