Research was performed to assess the effectiveness of a dynamic speed feedback sign (DSFS) as a speed reduction countermeasure when installed at horizontal curves on rural highways. It was of particular interest to assess whether the DSFS effectiveness varied based on curve advisory speed and to identify the optimal DSFS placement location with respect to the curve. A series of field evaluations were performed at five horizontal curves located along two-lane rural state highways in northern Michigan possessing posted speed limits of 65 mph and curve advisory speeds varying between 25 and 60 mph. The DSFSs were installed and evaluated at two different locations at each curve: 1. at the curve advance warning/advisory speed sign and 2. at the point of curvature. Vehicle speeds were tracked along the approach to each curve using handheld LIDAR guns. The results indicate that the DSFS was generally more effective at reducing motorists’ speeds when installed near the advance curve warning sign. Furthermore, the DSFS was more effective at locations with sharper curvature (i.e., lower advisory speeds). Continued use of DSFSs as a speed reduction countermeasure on rural horizontal curves is recommended, particularly at locations with a significant differential (e.g., at least 25 mph) between the upstream speed limit and the curve advisory speed. The DSFS should be positioned near the advance curve warning/advisory speed sign to provide adequate time for drivers to react and decelerate before reaching the curve.
Research was conducted to assess the effectiveness of a dynamic speed feedback sign (DSFS) as a speed reduction strategy at speed transition zones along five high-speed rural highways in northern Michigan. The DSFS was positioned on the shoulder in advance of the reduced speed limit at each community and was programmed to display speeds of approaching vehicles alternating with the upcoming reduced speed limit. Using handheld LIDAR guns, vehicle speeds were tracked through each speed transition area before and after installation of the DSFS. The DSFS was found to have a significant speed reduction effect throughout each of the five speed transition zones. The speed reductions generally began when the DSFS came into the motorists’ view, and the speed reduction effect increased as motorists approached DSFS. The greatest speed reduction effects were observed at the DSFS location itself, where speeds were 3.2 to 7.8 mph lower with the DSFS present, and these reductions were sustained on entry to the community. Similarly, drivers were 78.8 to 92.4% less likely to exceed the reduced speed limit with the DSFS present. Positioning the DSFS further upstream typically resulted in earlier speed reductions, although this effect became negligible once vehicles reached the reduced speed zone entering the community. Based on the study findings, continued use of DSFS for speed management at speed transition zones entering communities on high-speed rural roadways is recommended. When used in this context, the DSFS should be positioned 250 to 650 ft upstream of the reduced speed limit.
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