Study On The Mechanism Of Multiple-Vehicle Collision On Highway Under Fog Weather Condition

Rear-end is one of the most common type of highway collision,and foggy weather is one of the important causes of the collisions.And as a result of the continuous and rapid characteristics of the highway traffic flow,and the limited visibility of foggy weather environment,once the collision happened,the multiple-vehicle rear-end collision might occurred on account of the untimely collision avoidance of the rear vehicles.The multiple-vehicle rear-end collision could result in serious consequences and make the traffic flow in highway become blocked.Considering the idealized characteristic of theoretical derivation method and the inaccuracy characteristic of statistical regression method based on the historical collision data,this paper proposes the innovative research method,that is using the driving simulator which could support multiple drivers on-online interaction and at the same time.The study on the mechanism of multiple-vehicle rear-end collision on highway and the effectiveness of the speed limit control measures under fog weather condition have been conducted.TTC(Time-To-Collision)is chosen as the surrogate safety measures index.In order to evaluate the rear-end collision risk,the risk level is divided into three grades:high,middle and low.And the risk propagation model of rear-end collision in foggy weather is established.In the study of the influence of the foggy environment on the multiple-vehicle rear-end collision,it was found that the low space headway caused by the limited visibility is the most important reason for the rear-end collision.Fog environment will make drivers perceive higher levels of potential collision risk.In order to reduce the possibility of collision,the deceleration mode and behavioral variables change in the process of collision avoidance.Although the drivers have taken some compensation behavior,the frequency and severity of the multiple-vehicle rear-end collision are positively correlated with the fog level.Collision risk quantitative analysis showed that the influence of the light fog condition(visibility 150 m)on the collision risk is limited,but the heavy fog condition(visibility 60 m)makes a dramatic rise in risk of he multiple-vehicle rear-end collision,and the impact should not be ignored.In the study of the effectiveness of the speed limit control on the risk of multiple-vehicle rear-end collision,the improvement effect of the speed limit control is not obvious in the light fog environment.In the heavy fog environment,the speed limit control is very effective for the improvement of the collision risk.The reduction of the speed limits causes that the drivers tend to have a significant reduction in risk level of the subjective perception and compensation behaviors.When the speed limit is reduced to 60km/h,the rear-end collision will no longer occurr.Collision risk quantitative analysis also shows that the speed limit,can reduce the risk of the rear-end collision to a certain extent,especially the higher level of collision risk.What's more,it can greatly reduce the time length under high collision risk.According to the results of the risk analysis of the rear-end collision,combined with the questionnaire results,80km/h and 60km/h are selected as the recommended speed limit values in the light fog environment and the heavy fog environment.In the study of the collision differences of the vehicles in the same motorcade,the second car is at the highest risk of multiple-vehicle rear-end collision,the collision risk levels of other cars show a trend of fluctuations.Based on the behavior variables in the process of collision avoidance and external factors,using Logistic regression method,the risk propagation model of the multiple-vehicle rear-end collision is established,and the model prediction accuracy is high.