Rural variable speed limits : phase II.

Rural variable speed limits : phase II.

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Rural variable speed limits : phase II.
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    The Wyoming Department of Transportation (WYDOT) installed its first variable speed limit (VSL) corridor along Interstate 80 in the Elk Mountain Corridor in the Spring of 2009 in an effort to improve safety and reduce road closures, particularly during winter storm events. Since that time, four additional variable speed limit corridors have been implemented; three additional corridors along segments of Interstate 80 and one on WY 28, a rural two lane highway through the area of South Pass. There were three main objectives to this research effort: develop control strategy for the operation of VSL corridors, analyze the safety effects of the VSL system, and determine the impacts of the VSL on driver speed behavior. For the development of a control strategy, both weather and speed variables were considered. Initially a simple linear regression approach was considered but the complexity of the weather and speed behavior led to a regression tree based control strategy with a self-learning feedback loop using machine learning. For the safety task, descriptive baseline safety was analyzed for all five corridors. Since the Elk Mountain Corridor is the only VSL system in operation for more than two winter seasons, it was used for an Empirical Bayes (EB) before and after analysis, which indicated some statistically significant changes in crash frequency for just a few of the corridor segments. A weather-based safety analysis was performed on the four interstate VSL corridors and results from this analysis indicate a statistically significant reduction in crashes after the VSLs were implemented. Analyses of speed variables indicate a reduction in speed variation with the implementation of the VSL system. Modeling of the difference between observed and posted speeds show a reduction in speed compliance related to large reductions in posted speed limits.
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