Study Details

Study Title: The Effect of Median Design on Rural Freeway Safety - Flush Medians with Concrete Barriers and Depressed Medians

Authors: Tarko, A.P. et al.

Publication Date: JAN, 2008

Abstract: Although median barriers are an absolute means of preventing drivers from crossing road medians and colliding with vehicles moving in the opposite direction, they may cause additional crashes. This perhaps complex safety effect of median barriers has not been well investigated. Being able to predict the safety impact of most types of median barriers on rural freeways is becoming more and more desirable because some state Departments of Transportation plan to expand many of their four-lane rural freeways to six lanes to accommodate the increases in traffic volume. Realistic crash prediction models sensitive to the median design would provide the needed guidance useful in designing adequate median treatments on widened freeways. The impact of median designs on crash frequency was investigated in our study through Negative binomial regression and before-and-after studies based on data collected in eight participating states. The impact on crash severity was investigated with a logit model. The separate effects of changes in median geometry were quantified for single vehicle (SV), multiple vehicle same direction (SD), and multiple vehicle opposite direction (OD) crashes. The results were significantly different and indicated that reducing the median width without adding barriers (the remaining median width is still reasonably wide) increases the severity of crashes, particularly OD crashes. Further, reducing the median and installing concrete barriers eliminates the OD crashes but doubles the frequency of SV crashes while tending to lessen the frequency of SD crashes. The crash severity also tends to increase.

Study Citation: Tarko, A.P., Villwock, N.M., Blond, N. (2008). The Effect of Median Design on Rural Freeway Safety - Flush Medians with Concrete Barriers and Depressed Medians. 2008 Annual Meeting of Transportation Research Board CD Compendium of Papers.


CMFs Associated With This Study

Category: Roadside

Countermeasure: Install concrete guardrail in median

CMF CRF(%) Quality Crash Type Crash Severity Roadway Type Area Type
2.2 -120 4 Stars Single vehicle All Principal Arterial Other Freeways and Expressways Rural
0.8 20 4 Stars Sideswipe All Principal Arterial Other Freeways and Expressways Rural
0 100 4 Stars Cross median,Frontal and opposing direction sideswipe,Head on All Principal Arterial Other Freeways and Expressways Rural