Study Details

Study Title: Safety Evaluation of Change in Posted Speed Limit From 65 MPH to 70 MPH on Rural Virginia Interstate System

Authors:

Publication Date:JAN, 2018

Abstract: Effective July 1, 2010, the Virginia Department of Transportation (VDOT) increased the maximum allowable posted speed limit on interstates and similar facilities from 65 mph to 70 mph, if recommended after an engineering study. As a result, VDOT performed engineering studies on selected rural interstates posted at 65 mph. Subsequently, by November 2010, VDOT increased the speed limit from 65 to 70 mph for approximately 670 centerline miles of select rural interstates. There is a need to understand the safety and operational effects of increasing posted speed limits from 65 to 70 mph. This paper presents the results of an Empirical Bayes before-after study. The analysis was based on four years of data before and after the increase in posted speed limit, focusing on total, injury, run-off-road, and truck-related crashes. Safety performance functions were estimated and used to account for changes in traffic volume. Comparison segments were used to develop annual adjustment factors, account for regional differences, and identify underlying crash trends in the period before the increase in speed limit. The study considered both aggregate and disaggregate effects. At the aggregate level, the results indicate no increase in any of the focus crash types after the increase in posted speed limit. Focusing on sites without other changes, which are most indicative of the impacts of the increased speed limit, the increased speed limit did not change (i.e. increase or decrease) any of the crash types. The disaggregate analysis provides further insight into the circumstances where the change in posted speed limit had more and less pronounced impacts. Specifically, the disaggregate analysis showed that segment type (base or interchange) influenced the safety impact; interchange segments observed statistically significant increases in total, run-off-road, and truck-related crashes. The disaggregate analysis also showed that roadway improvements (e.g., rumble strip installation/reinstallation, pavement resurfacing activity, guardrail, pavement markings, and various warning signage) may help to offset the safety impact of increasing the posted speed limit.

Study Citation: Himes, S., F. Gross, M., Nichols, and M. Lockwood. "Safety Evaluation of Change in Posted Speed Limit From 65 MPH to 70 MPH on Rural Virginia Interstate System". Presented at the 97th Annual Meeting of the Transportation Research Board, Paper No. 18-01486, Washington, D.C., (2018).


CMFs Associated With This Study

Category: Speed management

Countermeasure: Increase speed limit from 65 mph to 70 mph

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.239-23.94 StarsAllAllPrincipal Arterial InterstateRural
0.9644 StarsAllAllPrincipal Arterial InterstateRural
1.035-3.54 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.87412.64 StarsAllK,A,B,CPrincipal Arterial InterstateRural
1.141-14.14 StarsRun off roadAllPrincipal Arterial InterstateRural
0.89710.34 StarsRun off roadAllPrincipal Arterial InterstateRural
1.207-20.74 StarsTruck relatedAllPrincipal Arterial InterstateRural
0.9821.84 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.007-0.74 StarsAllAllPrincipal Arterial InterstateRural
0.9138.75 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.9861.44 StarsRun off roadAllPrincipal Arterial InterstateRural
1.005-0.54 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.007-0.74 StarsAllAllPrincipal Arterial InterstateRural
0.9346.64 StarsAllK,A,B,CPrincipal Arterial InterstateRural
1.017-1.74 StarsRun off roadAllPrincipal Arterial InterstateRural
0.02797.34 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.038-3.84 StarsAllAllPrincipal Arterial InterstateRural
0.9544.64 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.9762.44 StarsRun off roadAllPrincipal Arterial InterstateRural
1.076-7.64 StarsTruck relatedAllPrincipal Arterial InterstateRural
0.9970.34 StarsAllAllPrincipal Arterial InterstateRural
1.237-23.75 StarsAllAllPrincipal Arterial InterstateRural
0.9188.25 StarsAllK,A,B,CPrincipal Arterial InterstateRural
1.118-11.84 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.9415.95 StarsRun off roadAllPrincipal Arterial InterstateRural
1.158-15.85 StarsRun off roadAllPrincipal Arterial InterstateRural
0.9881.24 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.544-54.45 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.006-0.64 StarsAllAllPrincipal Arterial InterstateRural
0.9970.34 StarsAllAllPrincipal Arterial InterstateRural
1.098-9.85 StarsAllAllPrincipal Arterial InterstateRural
1.099-9.95 StarsAllAllPrincipal Arterial InterstateRural
0.9861.44 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.9376.34 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.9138.74 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.9584.24 StarsAllK,A,B,CPrincipal Arterial InterstateRural
0.9554.54 StarsRun off roadAllPrincipal Arterial InterstateRural
0.9683.24 StarsRun off roadAllPrincipal Arterial InterstateRural
1.017-1.74 StarsRun off roadAllPrincipal Arterial InterstateRural
0.9914 StarsRun off roadAllPrincipal Arterial InterstateRural
1.012-1.24 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.093-9.34 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.013-1.34 StarsTruck relatedAllPrincipal Arterial InterstateRural
1.234-23.45 StarsTruck relatedAllPrincipal Arterial InterstateRural