Study On Speed Limit Value Of Freeway Incident Area

With the increase of freeway mileage,traffic incident depended on the freeway began to increase.The increasing of the traffic incident could affect the driver's driving safety and easy to cause the secondary accidents,reduce the use efficiency of freeway.But it's necessary for speed setting near the area road;the reasonable speed limit values of area can juggle the driver's safety and road use efficiency.This paper focuses on the characteristics of traffic system of freeway,combing traffic organizational forms,and solves the problems that what the limited speed acquired when the traffic incident occurred in the basic and ramp of freeway.The relationship was analyzed in speed discreteness of the area road and the accident rate.The relationship was studied in the queue length and the vehicle speed of the upstream zone.Conflict rate and queue length were selected respectively as the characterization of safety and efficiency index.Cellular automata,as a concise and effective model,have unique advantages in traffic flow modeling.Based on single-lane NaSch model,a two-lane cellular model is established to describe all kinds of lane-changing rules,driving behaviors and special sections.A two-lane cellular automata model rules and the simulation program were set up,and change law of conflict rate and queue length with the different speed limit values was obtained.According to different sensitivity of the safety and efficiency to the change of speed limit,make both dimensionless,weighted average method was used to calculate the optimal speed limit.The results show that at the level of second service,the speed limit value of the basic section is 70km/h.At the level of third service,the speed limit value is 60km/h;in connected section of ramp and main line,at the level of second service,the speed limit value of incident area is 60 km/h.At the level of third service,the speed limit value of incident area is 50 km/h.