Mountainous expressways are characterized by complex topography, resulting in extensive combined horizontal–vertical alignment sections where vehicle dynamics are more complex and the following risks are elevated. In such environments, vehicle car-following behavior is jointly influenced by inter-vehicle interactions and road geometric constraints, which limit the applicability of traditional car-following models.
To address this issue, a Mountainous Combined-Alignment Car-Following Model (MCCM) is proposed based on driving risk field theory. The model constructs a vehicle kinetic energy field incorporating slope and curvature to describe the effects of combined alignments on vehicle motion, and integrates it with the road potential energy field and driver behavior field to form a unified driving risk field. The short-range interaction characteristics of the risk field are transformed into forces acting on the following vehicle, enabling simultaneous representation of vehicle dynamics, driver behavior, and inter-vehicle interactions.
Measured trajectory data from a typical combined-alignment section of the Hangrui Expressway in Yunnan Province are used for model calibration and validation. Model performance is evaluated using the root mean square error (RMSE) and mean absolute percentage error (MAPE), and compared with the Intelligent Driver Model (IDM) and Safety Potential Field Model (SPFM). Results indicate that MCCM achieves higher accuracy in trajectory fitting, acceleration–deceleration response, and car-following stability, with significantly lower errors than the reference models. The proposed model provides effective support for driving safety analysis and microscopic traffic simulation on mountainous expressways.