Runaway Truck Warning and Detection System Installed at Colorado Truck Escape Ramps Reduced Total Crash Frequency by 41 Percent and Severe Injury Crashes by 39 Percent.
Observational Before and After Study in Colorado Found Reductions in Total Crashes and Severe Crashes.
Colorado, United States
Evaluation of Feasibility of Deployment of Runaway Truck Detection and Warning Systems at Truck Escape Ramps
Summary Information
Truck escape ramps (TERs), typically found on routes with mountainous downgrades, help to safely contain and stop runaway commercial vehicles. This study evaluated the safety performance of experimental signing, detection and warning system for TRE using an observational before and after analysis. The safety evaluation focused on a 7.9-mile segment at Wolf Creek Pass on westbound SH-160A. Advanced warning diagrammatic signs of hairpin turns and escape ramp locations, as well as enhancement of signs with flashing beacons and “blank-outs” (i.e., LED messages that only display when activated) were implemented at Wolf Creek Pass in 2018. The study also evaluated the feasibility of deployment of this system at all TERs in Colorado.
METHODOLOGY
To evaluate the effectiveness of TER at the Wolf Creek Pass corridor on safety, the study conducted an observational before-and-after analysis using empirical Bayes method to correct for the regression to the mean bias. TER on the selected segment was constructed in 2018. The crash data analyzed was from 2014 to 2017 for the before period, and from 2019 to 2022 for the after period. The Safety Performance Function (SPF) was used to estimate expected crash frequency and severity based on traffic levels for similar facilities. In addition, the Level of Service of Safety (LOSS) which classifies roadway safety by comparing observed crashes to SPF-predicted values was applied.
FINDINGS
The crash analysis found that the following safety improvements occurred even with an increase of approximately 9 percent in traffic volume on the corridor (i.e., a reduction in crash rate from 3.76 to 2.03 crashes per million vehicle miles travelled (VMT)).
- The total number of crashes on the segment decreased from 129 to 76, a reduction of 41 percent.
- Injury-related crashes decreased from 36 to 19 (47 percent). The number of injured people decreased from 39 to 28 (28 percent).
- The number of people killed increased from 2 to 3 (50 percent).
- Crashes involving property damage only decreased from 91 to 54.
- The disparity in crashes involving westbound vehicles fell from 79.8 percent to 64.5 percent.
- The number of commercial vehicles involved in crashes decreased from 51 to 23 (30 percent).
- For the westbound direction, LOSS moved from the high LOSS IV (high potential for crash reduction) range for total crashes into the low LOSS IV range. LOSS moved from the LOSS IV range to the LOSS III range (moderate to high potential for crash reduction) for severe crashes.
