Evaluating Driver Response to a Dynamic Speed Feedback Sign at Rural Highway Curves

Abstract

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.