Abstract: The unreasonable combination of length and grades of slopes leads to undesirable reduction of heavy-duty vehicles′speeds in mountain areas.Even worse,it would result in serious traffic accidents.Based on force conditions and operational characteristics in climbing processes,a kinetic model is developed with a case study of a heavy-duty vehicle. With the restriction of climbing abilities,the characteristics of climbing and regulations of speed reduction of a fully load-ed heavy-duty vehicle are simulated.With a certain power-to-weight ratio,the profiles of this vehicle′s climbing speed are explored,using slope gradients and approaching speeds as two controls respectively.The attenuation curve of speeds shows that the approaching speed is positively related to the critical length of slopes,but has no influence on the steady climbing speed.For this heavy-duty vehicle with a low climbing performance,when the approaching speed is 80 km/h, the critical length is restricted to 400 m;while the speed is 60 km/h,the critical length is restricted less than 300 m, which are less than the corresponding value in current national standard Technical Standard of Highway Engineering . Therefore,when the speed reduction exceeds 20 km/h in climbing processes,it is necessary to set climbing lanes or rele-vant facilities,which is also given according to the simulation result.