Evaluation of Median Barrier Safety Issues
Creators: name: Agent, Kenneth R.
name: Pigman, Jerry G.
Publisher: name: Kentucky Transportation Center, University of Kentucky
Year: 2008
Subjects: subject: Transportation Engineering

description: The objective of this study was to evaluate the effectiveness of the Brifen TL-4 and Trinity CASS median cable barrier systems in preventing cross-median collisions on sections of I-64, I-71, and I-265 (Brifen system) and I-265 (Trinity system) in Jefferson County and on KY 4 (Brifen system) in Fayette County. An effort was made to identify crashes which involved a vehicle crossing a median. Using specific logic to identify this type of crash, 392 crashes were identified for the five-year period of 2001 through 2005. Using crash and mileage data resulted in an average of 0.28 crossover crashes per mile in the five years and an average of 0.05 fatal crossover crashes per mile. Using a statistical test, critical numbers of 0.35 cross-median crashes per mile per year for crashes of any severity and 0.20 fatal crashes involving cross-median crashes per mile per year were recommended as guidelines for median barrier applications. The study involved an evaluation of 325 crashes with a police reports obtained for 185 of the crashes. The large majority of the crashes where a police report was not located involved a minor impact where the vehicle probably continued with no report. The number of damaged posts ranged from one to 70 with an average of about six posts. A tractor trailer was involved in the crash where 70 posts were damaged. Only 29 of the 325 crashes (8.9 percent) resulted in a reported injury related to the impact with the cable system with no fatalities. There were 61 crashes in which the vehicle crossed the median before contacting the cable system; therefore, these crashes would likely have resulted in a vehicle encroaching into the opposing lane. There were 96 additional crashes in which the vehicle collided with the cable system when it was positioned adjacent to the travel lane and an analysis of the crash (including variables such as the impact angle) indicated that the vehicle had a substantial probability of crossing the median into the opposing lane. This is an indication that in the approximate 21-month time period of the study (less for the KY 4 installation) the cable system prevented up to 157 encroachments into the opposing lanes. On these high volume and high speed roadways, an encroachment into the opposing lane has the possibility of resulting in a crash with a severe or fatal injury. The cable system was found to successfully redirect the vehicles. A wide range of types of vehicles hit the cable at consistently high speeds. In only three crashes (0.9 percent) did a vehicle continue through the cable system and into the opposing travel lanes. The successful performance of cable barrier, along with the ability to repair damage with no disruption of traffic, warrants expanded use of this type of median barrier. The analysis of crash data in Kentucky should be used to identify locations where this type of median barrier would be cost effective. This will involve determining locations which have had the highest concentration of cross-median crashes.