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Citation |
Sun X, Huang B, Ishak S, Wolshon B. J. Transp. Saf. Secur. 2009; 1(3): 169-180. |
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Copyright |
(Copyright © 2009, Southeastern Transportation Center, and Beijing Jiaotong University, Publisher Informa - Taylor and Francis Group) |
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DOI |
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PMID |
unavailable |
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Abstract |
The safety impact of differential speed limits (DSL) with a truck lane restriction was investigated on a 17 mile long elevated freeway segment over the Atchafalaya Basin in Louisiana that has been a subject of concern for the past decade due to sporadically occurring fatal crashes involving large trucks. Three before and after (B-A) methods were used in the current study: A naive B-A method, the improved B-A method, and the comparison group B-A method. The last two methods estimate the safety difference of a highway facility between, with, and without an intended treatment while taking into account other variables that may affect safety. Although all three methods show the reduction in truck and total crashes with DSL implementation, the naive method clearly underestimates the magnitude of the reductions in this case. Lack of traffic composition information makes the results from the comparison group B-A method less reliable than that by the improved B-A method. Based on the improved B-A method, that is more scientific, the expected reductions are 13% for total crashes and 77% for truck crashes. The implementation of DSL and a truck lane restriction on this segment of the freeway has served its purposes. |