Design Criteria for Clothoid Curve of Expressway Reconstruction Based on Driving Simulation

After lane expansion and design speed increases for expressway reconstruction, the clothoid curve of curve section without clothoid curve should be added, resulting in safety benefits and investment costs. The United States, Germany, and Japan agree that when the curve radius reaches a certain threshold, the clothoid curve cannot be set. The radius threshold of circular curve without clothoid curve in Chinese specifications is the minimum radius of circular curve without superelevation. The radius is large and conservative. The design criterion research of expressway clothoid curve was developed to meet actual engineering needs. The driving simulation test with different curve radius sections before and after the clothoid curve is carried out. Based on the stability of entry and exit circular curves, design criteria for clothoid curve is proposed. The radius threshold of circular curve without clothoid curve is determined by combining foreign specifications and driving simulation test results in China.