Abstract:The helical ramp is often taken as the scheme to connect the elevation difference between the two sides of the road because of restricts of road resource and other factors in the mountain city. Due to the lack of design criteria for helical ramps in existing studies, as a result, the design of helical ramp often follows the linear standard of circular ramp or even branch road. 7 helical ramps in the main urban areas of Chongqing are selected to carry out the natural driving experiments. The environmental model of road is established through Carsim simulation software to analyze and compare the key influencing factors to cause the trajectory offset of vehicles. The research result shows that when Carsim is used to establish the driver simulation model, the simulation result of closed-loop control mode is more reliable. The trajectory deviation occurs only when the simulation running speed exceeds the measured running speed by more than 62.5%. It is recommended to increase the design speed of helical ramp appropriately. The minimum circular curve radius in the design of some helical ramps can be properly reduced according to the practical situation. For the helical ramps with the lower design speed, the actual running speed can be increased by increasing the ultra-high value.
