Summary:
Research was undertaken to determine the effectiveness of various speed warning technologies across a variety of critical speed-change contexts in order to provide guidance to support future installation and operation of such treatments in Michigan. The speed warning technologies evaluated in this research included dynamic speed feedback signs (DSFS), a flashing LED chevron system, a weather-activated slippery curve warning system, and targeted winter weather messages on changeable message signs (CMS). The speed reduction effectiveness of the selected speed warning technologies was assessed through a series of field evaluations performed at 21 highway locations representing various speed-change contexts, which included: freeway exit ramps (DSFS), mainline freeway curves (DSFS), rural highway curves (DSFS, flashing LED chevrons, weather-activated slippery curve warning system), transition from rural highway into a community (DSFS),transition from freeway to non-freeway (DSFS), and at bridges susceptible to winter icing (CMS messaging). The messaging strategies, warning alerts, and installation positions for each evaluation were selected based on the highway context and warning technology being evaluated. Speeds of free-flowing vehicles were tracked using LIDAR under existing baseline conditions and after the installation of the specified sign treatments. The primary measure of effectiveness was the speed reduction for each test sign condition compared to the existing signing. Overall, the study concluded that enhanced speed warning signing technologies can contribute to meaningful speed reductions in critical areas. The magnitude of the speed reductions varied based on the context, although speed reductions of up to 3.5 mph were observed at both horizontal curves and speed limit transition areas after the installation of the selected enhanced warning sign treatment. Similarly, drivers were 50 to 75 percent less likely to exceed the curve advisory speed or posted speed limit (or some increment above those speeds) after treatment installation. Typically, the greatest speed reductions were observed for drivers approaching at higher-than-average speeds, which is typically the group most targeted by the installation of such treatments. Based on the study findings, the continued use of the tested speed warning technologies is recommended for the highway contexts evaluated in this study. A series of specific recommendations related to sign characteristics, operational performance, and installation details are provided within the project report for each road context. The recommendations comply with the requirements of the 11th Edition of the Manual on Uniform Traffic Control Devices (MUTCD), which provides considerably greater restrictions towards the utilization of DSFS compared to prior editions. The recommendations may be utilized by MDOT and other transportation agencies towards the development of implementable guidelines, standards, and/or provisions for the use of speed warning technologies at freeway and non-freeway horizontal curve applications, speed limit transition areas, and CMS messaging during winter weather conditions.
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