Study Details

Study Title: Crash Modification Factors for Adaptive Traffic Signal Control: An Empirical Bayes Before-After Study

Authors: Tang et al.

Publication Date:SEP, 2020

Abstract: Adaptive traffic signal control (ATSC) is a novel traffic management system that is often deployed at high-­volume intersections in order to mitigate traffic congestion and improve travel time reliability. While past studies have demonstrated its operational effectiveness, relatively few have focused on safety performance. Those that have tend to suffer from limitations including small sample sizes, insufficient study designs, or the lack of consideration of potential temporal and corridor effects after ATSC installation. Furthermore, results from previous studies are mixed: while many studies point to a safety improvement, more recent studies seem to indicate that ATSC systems might increase crash frequency. In light of this, a comprehensive Empirical Bayes (EB) before-after observational study was conducted using ATSC data collected throughout Pennsylvania. Crash modification factors (CMFs) were estimated based on the following different case scenarios: crash severity levels and crash types (total, fatal and injury, rear-end, and angle crashes); intersection locations (all intersections and intersections along corridors only); and, intersection configurations (3-leg and 4-leg). Temporal trends for in­tersection-level CMFs were examined using annual crash data in the after period. Corridor-level CMFs were also developed to quantify changes in safety performance along corridors with ATSC installed. The results suggest that ATSC is associated with a nominal increase in total and angle crashes, and an expected decrease in fatal plus injury crashes and rear-end crashes. However, the results were not statistically significant. The safety effect estimates are similar when considering intersection locations and configurations. In addition, the temporal trend analysis indicates that the safety effectiveness does not vary annually in the after period, suggesting no obvious novelty effect associated with ATSC. Finally, the magnitude of the corridor-level CMFs are slightly lower than the intersection-level CMFs, except for rear-end crashes.

Study Citation: Tang, H., V.V. Gayah, and E.T. Donnell. "Crash modification factors for adaptive traffic signal control: An Empirical Bayes before-after study". Accident Analysis and Prevention, Vol. 144, (2020).

Related Citations: Tang, H., V.V. Gayah, and E.T. Donnell. "Crash Modification Factors for Adaptive Traffic Signal Control: An Empirical Bayes Before-After Study". Presented at the 100th Annual Meeting of the Transportation Research Board, Paper No. 21-00179, Washington, D.C., (2021).

Study Report: Download the Study Report Document

CMFs Associated With This Study

Category: Intersection traffic control

Countermeasure: Install adaptive traffic signal control

CMF CRF(%)QualityCrash TypeCrash SeverityRoadway TypeArea Type
1.078-7.84 StarsAllAllAllUrban and suburban
0.9950.53 StarsAllK,A,B,CAllUrban and suburban
0.9913 StarsRear endAllAllUrban and suburban
1.142-14.24 StarsAngleAllAllUrban and suburban
1.071-7.14 StarsAllAllAllUrban and suburban
0.9980.23 StarsAllK,A,B,CAllUrban and suburban
0.9861.43 StarsRear endAllAllUrban and suburban
1.127-12.74 StarsAngleAllAllUrban and suburban
1.011-1.13 StarsAllAllAllUrban and suburban
0.84315.74 StarsAllK,A,B,CAllUrban and suburban
0.9910.93 StarsRear endAllAllUrban and suburban
0.9940.63 StarsAngleAllAllUrban and suburban
1.091-9.14 StarsAllAllAllUrban and suburban
1.03-33 StarsAllK,A,B,CAllUrban and suburban
0.9871.33 StarsRear endAllAllUrban and suburban
1.175-17.54 StarsAngleAllAllUrban and suburban
1.097-9.74 StarsAllAllAllUrban and suburban
0.9980.23 StarsAllK,A,B,CAllUrban and suburban
1.031-3.13 StarsRear endAllAllUrban and suburban
1.148-14.84 StarsAngleAllAllUrban and suburban
1.06-64 StarsAllAllAllUrban and suburban
0.9930.73 StarsAllK,A,B,CAllUrban and suburban
1.055-5.54 StarsRear endAllAllUrban and suburban
1.1-104 StarsAngleAllAllUrban and suburban