EFFECTS OF CONTINUOUS MEDIAN BARRIERS ON HIGHWAY SPEEDS, EMERGENCY RESPONSE TIMES, AND TRANSPORT TIMES ON NORTH CAROLINA HIGHWAYS

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. Consistent with the results obtained from the speed models, the results from the models estimated for crash frequency do not support the hypothesis that sections with continuous median barriers are associated with a larger number of speed related crashes compared to other median types. In order to assess the effect of median barriers on response times, several emergency operators in cities and counties across North Carolina were contacted. Most emergency operators indicated that data on response times were not recorded on a consistent basis. However, the emergency operators also mentioned that the continuous median barriers did lead to delays in responding to events. Some did acknowledge that these barriers prevent severe across-median crashes and reduced their call volume. The study also surveyed several neighboring States to study their policies regarding median crossovers. None of the agencies were aware of problems due to illegal use of these crossover openings. This was confirmed by limited observations in four locations in North Carolina.