2019 Volume 5 Issue 4 Pages A_32-A_41
This study focuses on optimal pattern of spacing between marking lines of speed reduction markings (SRMs) installed on straight lane adjacent to transition curve section, in order to induce vehicles to reduce their speed safely before entering the curve. The aim of this study is to show evidence of how the spacing pattern of SRMs should vary according to the curve radius, considering a change in curve radius affecting the vehicle speed in the absence of SRMs, based on causal inference by a difference-in-differences method incorporating an instrumental variable method using field experiment data. Our findings are summarized as follows: In the case of relatively small radius of curvature (300 m in this study), the deceleration effect of pattern End, which is the pattern of spacing with greater decrease ratio (DR) between the lines in end section than in beginning section on the SRM-installed lane, is higher than that of pattern Beginning for drivers who are driving at the speed of about 90 to 100 km/h or at about 100 to 110 km/h. In the case of relatively large radius of curvature (600 m), the effect does not significantly differ between pattern End and pattern Beginning for the drivers.
