Abstract
Although speed differential has long been recognized as a contributing factor to highway crashes, its relationship with crash rate has not been quantitatively established. An analysis of the crash data collected from the Jingjintang Expressway, one of the first freeways to be built in China, reveals a clear association between speed gap and crash rate. A difference in average operating speed between large and small vehicles of 10 to 15 km/h, reflecting a specific traffic composition, is associated with an unusually high crash rate. The speed differential problem is worse in developing countries because of the huge demand for freight transportation. Overloading is a common problem on highways. Heavily loaded trucks cannot reach the minimum freeway speed and so cause other vehicles to change lanes frequently; the situation consequently increases crash risks. Analysis results strongly suggest that managing the speed gap between large and small vehicles would be the most crucial step in combating the highway crash problem.
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