Effects of Continuous Median Barriers on Highway Speeds, Emergency Response Times, and Transport Times on North Carolina Highways;Final rept. July 2001-June 2003

摘要

In 1998, the North Carolina Department of Transportation started introducing positive barriers on many freeway segments to reduce across-median crashes. Unless emergency crossovers are provided, the lack of breaks in the median barriers reduces the opportunity for law enforcement to turn around to apprehend a speeder. The objective of this study was to assess the effect of different types of median barriers on speeding, speed related crashes, and emergency response times. Spot speed data were collected during off-peak periods from 51 freeway segments in North Carolina with four types of medians: traversable medians with no barriers, continuous median barriers with frequent crossovers, continuous median barriers without crossovers or infrequent crossovers, and non-traversable medians. Statistical models were developed to study the effect of median barrier type on average speeds and the propensity to exceed the speed limit. The results do not support the hypothesis that continuous median barriers without crossovers lead to speeding. Statistical models were also developed to study the effect of median barrier type on the frequency of speed related crashes.