Study Details
Study Title: Evaluating the Safety Effects of Signal Improvements
Authors: Schultz et al.
Publication Date:JAN, 2014
Abstract: A large percentage of fatal and injury crashes on roadways occur at intersections. To aid in reducing these severe crashes traffic signals are often implemented. To truly understand whether the signal installations are helping to reduce severe crashes, there is a need to evaluate the effectiveness of the traffic signal improvements through the development of Crash Modification Factors (CMFs). Recent research has shown that traditional safety evaluation methods have been inadequate in developing CMFs. In recent years, Bayesian statistical methods have been utilized in traffic safety studies to more accurately analyze the effectiveness of safety improvements. The hierarchical Bayesian method is an advanced statistical technique that has the capability to account for the shortcomings of traditional methods and to more fully reflect the effectiveness of safety improvements.
This report uses a hierarchical Bayesian model to analyze the effectiveness of new traffic signal installations and modifications to existing traffic signals from permissive only phasing to protected/permissive left turn phasing through the development of CMFs for multiple scenarios. A benefit-to-cost (B/C) analysis was also performed for each improvement to determine how long it would take to recover the cost of installation. The results showed that there was a slight increase in overall and non-severe crashes and a decrease in severe crashes for both new signal installations and modifications to existing signals. The B/C analysis indicated that there is a benefit to both improvements and that new signal installation costs can be recovered in approximately 5 years, while the installation of a left-turn signal modification can be recovered in approximately 9 weeks.
Study Citation: Schultz, G.G., M.Saito., A.L.Dowell., and C.S.Reese., Evaluating the Safety Effects of Signal Improvements. Presented at the 93rd Annual Meeting of the Transportation Research Board, Washington, D.C., (2014).
CMFs Associated With This Study
Category: Intersection traffic control
Countermeasure: Change permissive left-turn phasing to protected/permissive
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1.11 | -11 |  | All | | All | Not specified |
| 1 | 0 | | All | | Minor Arterial | Not specified |
| 1.26 | -26 | | All | | Principal Arterial Other Freeways and Expressways | Not specified |
| 1.02 | -2 | | Left turn | | All | Not specified |
| 0.67 | 33 | | Rear end | | All | Not specified |
| 0.13 | 87 | | Sideswipe | | All | Not specified |
| 0.51 | 49 | | All | | Minor Arterial | Not specified |
| 0.67 | 33 | | All | | Principal Arterial Other Freeways and Expressways | Not specified |
| 1.55 | -55 |  | Left turn | All | All | Not specified |
| 0.22 | 78 | | Head on | All | All | Not specified |
| 1.41 | -41 | | Sideswipe | All | All | Not specified |
| 0.97 | 3 | | All | All | Minor Arterial | Not specified |
| 1.24 | -24 | | All | All | Principal Arterial Other Freeways and Expressways | Not specified |
Countermeasure: Install a traffic signal
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|
| 1.16 | -16 | | All | | All | Not specified |
| 1.14 | -14 | | All | | Minor Arterial | Not specified |
| 1.71 | -71 | | All | | Principal Arterial Other Freeways and Expressways | Not specified |
| 0.52 | 48 | | Left turn | | All | Not specified |
| 0.64 | 36 | | Sideswipe | | All | Not specified |
| 0.62 | 38 | | All | | Minor Arterial | Not specified |
| 0.58 | 42 | | All | | Principal Arterial Other Freeways and Expressways | Not specified |
| 1.33 | -33 | | Left turn | All | All | Not specified |
| 0.43 | 57 | | Head on | All | All | Not specified |
| 1.15 | -15 | | Sideswipe | All | All | Not specified |
| 1.1 | -10 | | All | All | Minor Arterial | Not specified |
| 1.63 | -63 | | All | All | Principal Arterial Other Freeways and Expressways | Not specified |
| 1.63 | | | Left turn | | All | Not specified |
