Increases in heavy truck traffic on the expressway in recent years have raised concerns about safety and capacity in China. So there will be expressway with separation of cars and trucks and exclusive car ramps (ECR for short). At present, there are few researches on the design indicators of the ECR. Considering the actual situation of the development of the vehicle industry, this study revised the representative model size. According to the vehicle body movement theory and the Ackerman steering dynamics when the vehicle is turning, the calculation model of the widening value for the ECR is proposed. The MATLAB software is used to calculate the recommended widening value of the ECR based on the midline radius of the lane and the relationship between the radius and the widening value. Compared with the current widening value of the ramp in the “Guidelines for Design of Highway Grade-separated Intersections” in China, the result of this paper is concise and easy to use. It can provide reference for the design of ECR. keywords:expressway with separation of cars and trucks; exclusive car ramps; Ackermann steering geometry;

CICTP