United States Department of Transportation
i
I-80 Hybrid Regulatory Speed Limit Signing Design and VSL System Evaluation
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2021-02-01
[PDF-4.48 MB]
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Edition:Final Jun 2019 to Feb 2020
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Abstract:To improve traffic safety on a section of I-80 (through the mountains east of Salt Lake City) that experiences frequent periods of difficult weather, the Utah Department of Transportation (UDOT) implemented a Variable Speed Limit (VSL) zone (from MP 128.0 to MP 141.0 in both directions) using regulatory hybrid Changeable Message Signs (CMS). Originally, the CMS used white LED digits and black backgrounds. However, it was found that the visibility of those white digits that indicate speed limits has become a problem during inclement weather, especially snowstorms. During the summer season, strong sunlight can also affect the visibility of those white digits. To tackle this problem, UDOT has replaced the original CMS with amber/yellow digits for improved visibility. This research project aims to evaluate the effectiveness of the new CMS and perform a comprehensive before-and-after analysis of VSL system performance. The analysis is done by field trip video recordings, detector data analysis, and crash data examinations. Moreover, this research develops a road safety assessment model that takes occurrence data, road geometric features, and crash records as input. The model can be further used to predict road safety and the speed compliance rate improvement after the implementation of new CMS on other freeway corridors.
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