Study Details
Study Title: A Full Bayes Approach to Before-After Safety Evaluation with Matched Comparison
Authors: El-Basyouny and Sayed
Publication Date:JAN, 2010
Abstract: The full Bayes (FB) approach has recently been proposed for evaluating road safety treatments in before-after studies. Recognizing the advantages of the FB method and due to the lack of sufficient data to develop the safety performance function that is necessary to conduct an empirical Bayes study, the FB approach is used to determine the effectiveness of the Stop-Sign In-fill (SSIF) program of the Insurance Corporation of British Columbia (ICBC). The SSIF program funds the conversion from uncontrolled residential intersections to two-way stop controlled intersections in an alternating pattern. This alternating pattern provides consistency in the application of stop signs within a residential neighborhood. Different modeling formulations for the before-after evaluation were investigated and the results were compared with those of the traditional approach. No post-processing of the results is required to achieve the odds ratio. The FB analysis revealed an overall significant reduction in predicted collision frequency of 51.1% with the credible interval (36.8%, 62.3%) at the 0.95 confidence level. It was also found that incorporating such design features as matched yoked comparison groups in collision prediction models may significantly improve the fit, while reducing the need to account for over-dispersion. The results of the traditional technique were compatible with those of the FB approach at the overall-level. It seems that the random selection of sites, which reduces the RTM effect, is the reason that both approaches gave relatively similar overall-level results. However, the two methods produced quite different results at the zone (site)-level.
Study Citation: El-Basyouny, K., and T. Sayed., "A Full Bayes Approach to Before-After Safety Evaluation with Matched Comparison." Presented at the 89th Annual Meeting of the Transportation Research Board, Washington, D.C., (2010).
CMFs Associated With This Study
Category: Intersection traffic control
Countermeasure: Install two-way stop controlled intersections at uncontrolled intersections
| CMF | CRF(%) | Quality | Crash Type | Crash Severity | Roadway Type | Area Type |
|---|---|---|---|---|---|---|
| 0.489 | 51.1 |  | All | All | Local | Urban and suburban |
