Study Details

Study Title: Developing Crash Modification Factors for Variable Speed Limits

Authors: Avelar et al.

Publication Date:MAY, 2021

Abstract: The objective of this study was to perform rigorous safety effectiveness evaluations of variable speed limit (VSL) implementation on freeway corridors. To accomplish this objective, the research team compiled safety data from Virginia, Wyoming, and Georgia and used an interrupted time series study design (with a comparison group for Georgia). The team analyzed data using logistic and negative binomial generalized estimating equations models. The results from Wyoming and Georgia produced evidence of significant reductions in several types of crashes. The research team found total crash reductions of 34.4 and 29.2 percent associated with VSL installations in Wyoming and Georgia, respectively. The economic evaluation for these two States generally indicated larger benefits than costs. For Georgia, the estimated benefit–cost (B/C) ratio was 40.38. The economic analysis for Wyoming yielded a more modest B/C ratio of 9.05, though still indicating benefits outweighing VSL installation costs. Results from Virginia were inconclusive as the analysis found no statistical evidence of a change in overall safety. The inconclusiveness of these results is possibly due to the sample size of the after period, the small amount of time the system was active, and the manner in which the VSL was used in the corridor for enhancing safety during adverse weather conditions.

Study Citation: Avelar, R., E.S. Park, S. Ashraf, K. Dixon, M. Li, and B. Dadashova. "Development of Crash Modification Factors for Variable Speed Limits" Report No. FHWA-HRT-21-053. Federal Highway Administration, Office of Safety Research and Development. McLean, Virginia. (2021).

Related Citations: Tech Brief. "Development of Crash Modification Factors for Variable Speed Limits" Report No. FHWA-HRT-21-080. Federal Highway Administration, Office of Safety Research and Development. McLean, Virginia. (2021).

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Advanced technology and ITS

Countermeasure: Install Variable Speed Limit (VSL)

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.23-232 StarsAllAllPrincipal Arterial InterstateNot specified
0.87132 StarsAllAllPrincipal Arterial InterstateNot specified
1.2-202 StarsAllK,A,B,CPrincipal Arterial InterstateNot specified
1.22-222 StarsAllOPrincipal Arterial InterstateNot specified
1.78-782 StarsRear endAllPrincipal Arterial InterstateNot specified
1.43-432 StarsFixed objectAllPrincipal Arterial InterstateNot specified
1.1-102 StarsWet roadAllPrincipal Arterial InterstateNot specified
1.04-42 StarsOtherAllPrincipal Arterial InterstateNot specified
0.66343 StarsAllAllPrincipal Arterial InterstateNot specified
0.49513 StarsAllK,A,B,CPrincipal Arterial InterstateNot specified
0.71293 StarsAllOPrincipal Arterial InterstateNot specified
0.35653 StarsRear endAllPrincipal Arterial InterstateNot specified
0.34662 StarsRear endK,A,B,CPrincipal Arterial InterstateNot specified
0.59413 StarsFixed objectAllPrincipal Arterial InterstateNot specified
0.39612 StarsFixed objectK,A,B,CPrincipal Arterial InterstateNot specified
0.70829.23 StarsAllAllPrincipal Arterial InterstateNot specified
0.72827.22 StarsAllAllPrincipal Arterial InterstateNot specified
0.54745.32 StarsAllAllPrincipal Arterial InterstateNot specified
0.89113 StarsAllK,A,B,CPrincipal Arterial InterstateNot specified
0.9118.92 StarsAllK,A,B,CPrincipal Arterial InterstateNot specified
0.64835.22 StarsRear endAllPrincipal Arterial InterstateNot specified
0.82182 StarsRear endK,A,B,CPrincipal Arterial InterstateNot specified
1.01-12 StarsWet roadAllPrincipal Arterial InterstateNot specified