Road turning is the common traffic bottleneck, where the traffic accidents often happen. By analyzing the dynamic behaviors of vehicles in the road turning, the conditions of vehicles turning safely can be gained. Besides, numerical simulation the effects of the road turning with ultrahigh to the traffic flow by using the cellular automation model. The result shows that ultra-high can provide greater centripetal force and raise the speed of vehicles when they are turning and reduce the possibility of vehicles slipping towards outside incline. However, too much great of ultra-high exists the dangers of vehicles slipping and overturning towards the inside of road turning. Therefore, the reasonability of ultrahigh setting relate directly to the safety of vehicles moving.