Dilemma Zone in Two-lane Highways

Based on passing behavior analysis, this paper introduced the concept of a dilemma zone £¨DZ£© road segment, where a vehicle could not accomphsh overtaking or avoid collision with the oncoming vehicle in two-lane highways.Kinematics theory is used to establish the relationship between downstream vehicles£§ speeds, number of vehicles, design speed and the length of DZ. It is found that compared with the case of one overtaking one, the safe distance for overtaking a platoon is larger, and will increase with the design speed, the size and speed of platoon increasing. It is also found that a high flow or velocity can increase the probabilities of DZ appearance and accident rate resulted from drivers£§ wrong estimations. Finally, the conditions of safe overtaking such as speed limit and visual scope are proposed for safety driving strategy and precautions.