The Method of Road Safety Analysis Based on Two-Dimensional Speed Difference

Human, vehicle and road are three essential factors in transportation system. There is an important relationship between traffic accident and the system coordination under the normal driving condition. It can be verified by field experiments and calculation. The speed is an integrative index that appropriately shows the relationship among human, road and vehicle. Each vehicle has its own accelerating and decelerating movement by the two-dimensional form, which can be affected by road geometric and also has an impact on traffic accident. Based on vehicles' operational characteristics, authors use two-dimensional speed difference to show vehicles' movement law, and develop the road safety analysis and evaluation models and safety criteria for the horizontal alignment by using theory analysis and actual accident investigation method.