Speed Transition Zone Design Based on Driving Simulator Research

Large speed gaps may increase risks between adjacent speed zones. Therefore, a speed transition zone is designed to provide a smooth change between two highway segments with different speed limits. The purpose of this study is to establish a procedure for transitional speed zone design on two-lane roads by using drivers' behavioral statistics. In order to evaluate the effect of the speed limit zone on drivers' deceleration behaviors when passing different speed zones, two factors were considered in this study: existence of work zones and horizon curves. The speed gaps in this experiment are 50 km/h in work zone areas and 20 km/h respectively. By using randomly selected drivers, the study measured drivers' actions in a real vehicle under the simulated environment traveling between speed zones at a 0.03 second intervals. Several different measures of effectiveness were used to compare the characteristics of the speed distributions, including average speed, 85th percentile speed and pace speed. Results show that there is a significant difference in speed choice for deceleration between two scenarios due to speed reduction. The relationship between speed limit reduction and deceleration length is described by a linear model. The length of the deceleration section is estimated by the model. Results show that the deceleration section is positively correlated to speed reduction. The modeling process gives detailed guidance for the design of a transitional speed zone.