Abstract
Variable speed limit (VSL) and variable advisory speed (VAS) signs are efficient, cost-effective and among the state-of-the-art active traffic management (ATM) strategies. They adopt the idea of dynamically changing posted speed limits to improve highway safety performance and operation by harmonizing traffic speed. VSL/VAS system involves changing speed limits according to real-time traffic events and weather conditions. Hence, traditional average annual daily traffic (AADT) based crash prediction models may not capture the temporal effect of traffic characteristics due to the high level of aggregation. To address this issue, short-term safety performance functions (SPFs) with aggregation levels of average annual weekday hourly traffic (AAWDHT) and average annual weekday peak traffic (AAWDPT) along with AADT-based SPFs were developed using high-resolution traffic detector and VSL/VAS operational data. In this study, the Poisson log-normal model performed well at each level of aggregation and thus is recommended for developing short-term SPFs. In line with previous studies, traffic volume and standard deviation of speed were found to be positively associated with crash frequency in all the estimated models. In addition, it was found that implementation of VSL/VAS significantly reduced crash frequency by 15.97% and 26.14% for the AAWDHT and AAWDPT models, respectively. The safety improvement was captured in the short-term models in a more distinguished way than in the highly aggregated AADT-based model. The findings of this study pave the way for practitioners and policymakers to evaluate and select important parameters for VSL/VAS strategy implementation on freeways.
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Data Availability Statement
Some or all data, models, or code that support the findings of this study are available from the corresponding author upon reasonable request.
Acknowledgments
The authors would like to express their heartiest gratitude to Dr. Jinghui Yuan and Mr. Heesub Rim for their constructive suggestions and guidance throughout the study. Lastly, the authors highly appreciate the help from the Georgia and Oregon Departments of Transportation (DOTs) for providing data that was used in this study.
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Information & Authors
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Published In
Journal of Transportation Engineering, Part A: Systems
Volume 149 • Issue 3 • March 2023
Copyright
© 2022 American Society of Civil Engineers.
History
Received: Jan 26, 2022
Accepted: Oct 31, 2022
Published online: Dec 30, 2022
Published in print: Mar 1, 2023
Discussion open until: May 30, 2023
ASCE Technical Topics:
- Business management
- Engineering fundamentals
- Financial management
- Highway and road management
- Highway transportation
- Highways and roads
- Infrastructure
- Models (by type)
- Practice and Profession
- Traffic accidents
- Traffic engineering
- Traffic management
- Traffic models
- Traffic safety
- Traffic speed
- Transportation engineering
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