Study Details

Study Title: Safety Effects of Median Treatments Using Longitudinal Channelizers: Empirical Bayesian Before-and-After Study

Authors: Zhou et al.

Publication Date: DEC, 2013

Abstract: A new median treatment technique using longitudinal channelizers has been used in Florida as an alternative to the traditional permanent concrete barrier. However, the effects of the new technique on roadway safety and its economic performance have not been well documented. This paper's intent is to present the results of a comprehensive evaluation on the safety and economic performance of the longitudinal channelizers' median treatments with before-and-after crash data. Two types of longitudinal channelizers' treatments - full median opening to directional median opening and full median opening to left-in only median opening - were evaluated. To account for the site selection bias, the empirical Bayesian before-and-after study method was used. The safety performance function for roadway segments with full median openings was developed with the generalized linear model to consider the negative binomial distribution of the crash counts in population entities. The targeted crash types for the longitudinal channelizers' median treatment (the left-turn crashes) were reduced by approximately 60 and 45% in the after period for directional and left-in only median treatments, respectively. The economic performance of the longitudinal channelizers' median treatments was quantified based on the crash analysis results from the empirical Bayesian before-and-after study. The annual cost reductions on crashes per site location were $562,321 and $94,480 for directional and left-in only median treatments, respectively. Benefit-cost ratios of 18.9-224.9 can be achieved with the implementation of longitudinal channelizers' median treatments. Further application of longitudinal channelizers for median treatment is recommended, especially for those locations where immediate treatments for safety purpose are required.

Study Citation: H. Zhou, J. Zhao, P. Hsu and J. Huang, "Safety Effects of Median Treatments Using Longitudinal Channelizers: Empirical Bayesian Before After Study", Journal of Transportation Engineering, Vol.139,No.12,American Society of Civil Engineers,(2013)pp. 1149-1155


CMFs Associated With This Study

Category: Access management

Countermeasure: Convert an open median to a directional median

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
0.76 24 4 Stars All K,A Principal Arterial Other Urban and suburban
0.77 23 4 Stars All K,A,B,C Principal Arterial Other Urban and suburban
0.82 18 4 Stars All A Principal Arterial Other Urban and suburban
0.82 18 4 Stars All C Principal Arterial Other Urban and suburban
1.13 -13 3 Stars All O Principal Arterial Other Urban and suburban
0.93 7 3 Stars All All Principal Arterial Other Urban and suburban
0.43 57 3 Stars Left turn All Principal Arterial Other Urban and suburban

Countermeasure: Convert an open median to a left-in only median

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
1.31 -31 2 Stars All K,A Principal Arterial Other Urban and suburban
0.93 7 3 Stars All K,A,B,C Principal Arterial Other Urban and suburban
1.41 -41 2 Stars All A Principal Arterial Other Urban and suburban
0.8 20 3 Stars All C Principal Arterial Other Urban and suburban
1.13 -13 3 Stars All O Principal Arterial Other Urban and suburban
0.95 5 3 Stars All All Principal Arterial Other Urban and suburban
0.55 45 3 Stars Left turn All Principal Arterial Other Urban and suburban