Control Parameters for the Ramp and Speed-Change Lane of Urban Expressways

Abstract

Urban expressways can be built with various patterns, resulting in complex traffic conversions. In practice, implementing identical design control parameters under different patterns or traffic conditions is unreasonable, and further analysis is therefore necessary to improve the flow of traffic. Control parameters, regardless of whether they are reasonable, affect the safety and efficiency of urban expressways. Design speed and minimum curve radius are the control parameters of the ramp. Acceleration/deceleration lane length and width-transition length are the control parameters of the speed-change lane. The factors influencing the control parameters of the ramp and the speed-change lane can be determined by analyzing the characteristics of the entrance/exit. To elucidate the mechanism of effects of the design speed and the stopping sight distance on the minimum ramp radius, the effects of traffic flow rate and ramp design speed on the length of the speed-change lane and the width-transition were analyzed. Calculation models for the control parameters of the ramp and the speed-change lane were established based on kinematics theory, traffic flow theory, and probability theory. The following conclusions can be drawn from the analysis and calculation. The design speed of the ramp can be classified according to ramp patterns and the properties of urban roads connected by ramps on both ends. The minimum curve radius of the structure pattern ramp that meets the requirement of the stopping sight distance is greater than that determined by the side-way force coefficient. The calculated lengths for the two-lane acceleration lane and the width-transition under traffic flow are greater than that demanded by the current specifications.