Study Details

Study Title: Evaluation of Dynamic Speed Feedback Signs on Curves: A National Demonstration Project

Authors: Hallmark et al.

Publication Date: JAN, 2015

Abstract: Lane departure crashes are a significant safety concern. The majority of lane departure crashes occur on rural two-lane roadways, with a disproportionate number of these crashes on horizontal curves. Curve-related crashes involve a number of roadway and driver causative factors. A primary driver factor is speeding. Dynamic speed feedback sign (DSFS) systems are one method to reduce vehicle speeds and, consequently, crashes on curves. These systems show promise but they have not been fully evaluated on curves. The Center for Transportation Research and Education at Iowa State University conducted a national demonstration project to evaluate the effectiveness of two different DSFSs in reducing speed and crashes on curves at 22 total sites on rural two-lane roadways in seven States. The goal is to provide traffic safety engineers and other professionals with additional tools to manage speeds and crashes on rural horizontal curves more effectively. Data were collected before and at 1, 12, and 24 months after installation of the DSFS. On average, most sites had decreases in mean speeds, with decreases up to 10.9 miles per hour (mph) noted for both the point of curvature (PC) and center of curve (CC). Most sites experienced changes in 85th percentile speed of 3 mph or more at the PC, with the majority of sites having a decrease of 2 mph at the CC. The numbers of vehicles traveling 5, 10, 15, or 20 mph over the posted or advisory speed limit were also compared. Large reductions in the number of vehicles traveling over the posted or advisory speed occurred for all of the after periods at the PC and CC, indicating that the signs were effective in reducing high-end speeds, as well as average and 85th percentile speeds. A before-and-after crash analysis was also conducted, and crash modification factors (CMF) were developed. CMFs ranged from 0.93 to 0.95 depending on the crash type and direction of the crash.

Study Citation: Hallmark, S., N. Hawkins, and O. Smadi. "Evaluation of Dynamic Speed Feedback Signs on Curves: A National Demonstration Project." Report No. FHWA-HRT-14-020. Federal Highway Administration. McLean, Virginia. (January 2015).

Related Citations: Hallmark, S., Y. Qiu, N. Hawkings, and O. Smadi. "Crash Modification Factors for Dynamic Speed Feedback Signs on Rural Curves." Journal of Transportation Technologies, Vol. 5 (2015) pp. 9-23.

Study Report: Download the Study Report Document


CMFs Associated With This Study

Category: Advanced technology and ITS

Countermeasure: Install dynamic speed feedback sign

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.95 5 4 Stars All All Not specified Rural
0.93 7 4 Stars All All Not specified Rural
0.95 5 4 Stars Single vehicle All Not specified Rural
0.95 5 4 Stars Single vehicle All Not specified Rural