Study Details

Study Title: Analyzing Raised Median Safety Impacts Using Bayesian Methods

Authors: Schultz et al.

Publication Date: JAN, 2011

Abstract: Because traffic safety studies are not performed in a controlled environment such as a laboratory, but rather in an uncontrolled real world setting, traditional analysis methods often lack the capability to adequately evaluate the effectiveness of roadway safety measures. In recent years, however, advanced statistical methods have been utilized in traffic safety studies to more accurately determine the effectiveness of such measures. These methods, particularly Bayesian statistical techniques, have the capabilities to account for the shortcomings of traditional methods. Hierarchical Bayesian modeling is a powerful tool for expressing rich statistical models that more fully reflect a given problem than traditional safety evaluation methods could. This paper uses a hierarchical Bayesian model to analyze the effectiveness of raised median installations on overall and severe crash frequency in the state of Utah by determining the effect each has on crash frequency and frequency of severe crashes at study locations before and after installation of raised medians. Several sites where raised medians have been installed in the last 10 years were evaluated using available crash data. The results of this study show that the installation of a raised median is an effective technique to reduce the overall crash frequency and frequency of severe crashes on Utah roadways with results showing a reduction in overall crash frequency of 25 percent and frequency of severe crashes of 36 percent along corridors where raised medians were installed. The results also show that hierarchical Bayesian modeling is a useful method for evaluating effectiveness of roadway safety measures.

Study Citation: Schultz, G., Thurgood, D., Olsen, A., Reese, C.S., "Analyzing Raised Median Safety Impacts Using Bayesian Methods." Presented at the 90th Meeting of the Transportation Research Board, Washington, D.C., (2011).


CMFs Associated With This Study

Category: Access management

Countermeasure: Install raised median

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.61 39 4 Stars All All Not specified
0.56 44 4 Stars All K,A Not Specified