Evaluation of temporary ramp metering for work zone safety
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Ramp metering has been successfully implemented in many states and studies have documented its positive mobility and safety benefits. However, there have been no studies on the use of ramp metering for work zones. This thesis reports the results from the first deployment of temporary ramp meters in work zones in the United States. Temporary ramp meters were deployed at seven work zones in Missouri. Due to lack of crash data, this study uses video data to extract alternative safety measures such as driver compliance, merging behavior, speed differentials, lane changing, and braking maneuvers. This evaluation suggests that temporary ramp meters should only be deployed at work zone locations where there is potential for congestion and turned on only during periods of high congestion. In comparison to over 90% compliance rates of permanent ramp meters implemented in other states, field data showed compliance rates from 40.5% to 82.9% in temporary ramp meter. This suggested that non-compliance could be a major safety issue in the deployment of temporary ramp meters. The use of a three-section instead of a traditional two-section signal head used for ramp metering produced significantly higher compliance rates. This thesis then aggregated the data into groups to further analyze the effects of different factors such as platoons, commercial trucks, work zone type and work zone-ramp configuration. After analyzing general characteristics of mainline and ramp vehicle speed and speed differentials, this study then focused on findings for different comparison groups. The two comparison groups are “between two work zones” versus “before work zone” configuration and “left-lane closed” versus “right-lane closed” work zone type. Results indicated lower mean speeds of mainline and ramp vehicles and higher differentials when ramp metering was turned on. This is expected and again temporary ramp meters are recommended only where congestion occurs. Congestion will lead to lower mainline speeds thus lower speed differentials either with or without ramp metering. Finally, analysis of merging headways showed that temporary ramp meters were effective in separating platoons before vehicles merged into mainline. This produces more single-vehicle merging which requires shorter gaps and causes fewer impacts on the mainline traffic.