Study Details

Study Title: Multi-State Safety Evaluation of Intersection Conflict Warning Systems (ICWS)

Authors: Himes et al

Publication Date: JAN, 2016

Abstract: Intersection Conflict Warning Systems (ICWS) were selected for evaluation under the Federal Highway Administration (FHWA) Evaluation of Low-Cost Safety Improvements Pooled Fund Study. This strategy is intended to reduce the frequency of crashes by alerting drivers of conflicting vehicles on adjacent approaches at unsignalized intersections. The evaluation was based on a multistate database of geometric, traffic, and crash data obtained for four-legged rural two-way stop-controlled intersections equipped with ICWS in Minnesota, Missouri, and North Carolina. To account for potential selection bias and regression-to-the-mean, an empirical Bayes (EB) before-after analysis was conducted, using safety performance functions (SPFs) for reference groups of similar four-legged rural two-way stop-controlled intersections without ICWS installation. These SPFs also control for changes in traffic volumes over time and time trends in crash counts unrelated to the strategy. The aggregate results indicate statistically significant crash reductions at the five percent level for all crash types for two-lane at two-lane intersections and four-lane at two-lane intersections. For two-lane at two-lane intersections, the CMFs for total crashes, fatal and injury crashes, and right-angle crashes are 0.73, 0.70, and 0.80, respectively. For four-lane at two-lane intersections, the CMFs for total crashes, fatal and injury crashes, and right-angle crashes are 0.83, 0.80, and 0.85, respectively. The benefit-cost ratio estimated with conservative cost and service life assumptions is 27:1 for all two-lane at two-lane intersections and 10:1 for four-lane at two-lane intersections with post-mounted warning signs. The results suggest that the strategy, even with conservative assumptions on cost, service life, and the value of a statistical life, can be highly cost effective. As this is an evolving strategy, this study reflects installation practices to date.

Study Citation: Himes, S., F. Gross, K. Eccles, and B. Persaud. "Multi-State Safety Evaluation of Intersection Conflict Warning Systems (ICWS)". Presented at the 95th Annual Meeting of the Transportation Research Board, Paper No. 16-4225, Washington, D.C., (2016).

Related Citations: Safety Evaluation of Intersection Conflict Warning Systems (ICWS), Federal Highway Administration, Techbrief, FHWA-HRT-15-076, February, 2016.

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Signs

Countermeasure: Install an intersection conflict warning system (ICWS) with a combination of overhead and advanced post mounted signs (various messages) and flashers

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.704 29.6 5 Stars All All Not specified Rural
0.742 25.8 4 Stars All Fatal,Serious injury,Minor injury Not specified Rural
0.697 30.3 4 Stars Angle All Not specified Rural

Countermeasure: Install an intersection conflict warning system (ICWS) with overhead signs (various messages) and flashers at the intersection on major; loop on minor

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.74 26 5 Stars All All Not specified Rural
0.6 40 5 Stars All Fatal,Serious injury,Minor injury Not specified Rural
0.807 19.3 4 Stars Angle All Not specified Rural

Countermeasure: Install an intersection conflict warning system (ICWS) with overhead signs (various messages) and flashers at the intersection on minor; loop on major

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.892 10.8 4 Stars All All Not specified Rural
0.944 5.6 4 Stars All Fatal,Serious injury,Minor injury Not specified Rural
1.084 -8.4 4 Stars Angle All Not specified Rural

Countermeasure: Install an intersection conflict warning system (ICWS) with post mounted signs (various messages) and flashers at the intersection on minor; loop on major

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.886 11.4 3 Stars All All Not specified Rural
1.064 -6.4 3 Stars All Fatal,Serious injury,Minor injury Not specified Rural
1.247 -24.7 3 Stars Angle All Not specified Rural
0.69 31 4 Stars All All Not specified Rural
0.896 10.4 3 Stars All Fatal,Serious injury,Minor injury Not specified Rural
0.763 23.7 3 Stars Angle All Not specified Rural

Countermeasure: Install an intersection conflict warning system (ICWS) with post mounted signs (various messages) and flashers in advance of the intersection on major; loop on minor

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.519 48.1 5 Stars All All Not specified Rural
0.45 55 5 Stars All Fatal,Serious injury,Minor injury Not specified Rural
0.454 54.6 5 Stars Angle All Not specified Rural
0.745 25.5 5 Stars All All Not specified Rural
0.734 26.6 5 Stars All Fatal,Serious injury,Minor injury Not specified Rural
0.769 23.1 5 Stars Angle All Not specified Rural

Countermeasure: Install intersection conflict warning systems (ICWS) for four-lane at two-lane intersections

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.74 26 3 Stars All All Not specified Rural
1.05 -5 3 Stars All Serious injury,Minor injury Not specified Rural
0.64 36 3 Stars Angle All Not specified Rural
0.72 28 4 Stars All All Not specified Rural
0.55 45 4 Stars All Serious injury,Minor injury Not specified Rural
0.8 20 3 Stars Angle All Not specified Rural
0.89 11 4 Stars All All Not specified Rural
0.95 5 4 Stars All Serious injury,Minor injury Not specified Rural
0.88 12 4 Stars Angle All Not specified Rural
0.83 17 5 Stars All All Not specified Rural
0.8 20 5 Stars All Serious injury,Minor injury Not specified Rural
0.85 15 5 Stars Angle All Not specified Rural

Countermeasure: Install intersection conflict warning systems (ICWS) for two-lane at two-lane intersections

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.86 14 3 Stars All All Not specified Rural
0.53 47 3 Stars All Serious injury,Minor injury Not specified Rural
1.95 -95 3 Stars Angle All Not specified Rural
0.78 22 3 Stars All All Not specified Rural
1.09 -9 3 Stars All Serious injury,Minor injury Not specified Rural
0.77 23 3 Stars Angle All Not specified Rural
0.73 27 4 Stars All All Not specified Rural
0.69 31 4 Stars All Serious injury,Minor injury Not specified Rural
0.79 21 4 Stars Angle All Not specified Rural
0.73 27 5 Stars All All Not specified Rural
0.7 30 5 Stars All Serious injury,Minor injury Not specified Rural
0.8 20 5 Stars Angle All Not specified Rural

The information contained in the Crash Modification Factors (CMF) Clearinghouse is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in the CMF Clearinghouse. The information contained in the CMF Clearinghouse does not constitute a standard, specification, or regulation, nor is it a substitute for sound engineering judgment.