| With the increasingly close regional connection and the constant growth of traffic demand,the number of new or expanded multi-lane highways with more than six lanes in both directions is increasing day by day.As an important part of multi-lane highways cross section,hard shoulder is very important for emergency protection and safety management of multi-lane highways.When vehicles in the inner lane break down and other emergency situations,they can only park to the right hard shoulder through multiple lane changes,which will undoubtedly bring huge safety risks.Therefore,it is of great significance to study the impact of left hard shoulder with emergency stop function on traffic safety of multi-lane highways.In order to demonstrate the necessity of setting left hard shoulder on multi-lane highways,historical accident causes and lane distribution characteristics of general multi-lane highways in China were analyzed,and the rejection probability and lane change distance of vehicles in the innermost lane under ideal conditions were calculated by means of acceptable gap theory.Through the analysis of the main functions of the left hard shoulder on the multi-lane highways,it is concluded that the correlation between the left hard shoulder and traffic safety mainly includes two aspects: one is the impact of the left hard shoulder emergency stopping function on traffic safety,the other is the impact of the left hard shoulder side clearance change on the driving safety.In order to study the correlation between the emergency stopping function of the left hard shoulder and traffic safety,a two-way 10-lane highways was selected as the research object,and the safety benefit of the emergency stopping function was indirectly reflected by the accident rate of the damaged vehicles in the inner lane,and the logistic regression model was constructed for analysis.The significant safety benefit factors are truck ratio,v/C ratio and relative potential energy.On this basis,the use of the left hard shoulder with emergency parking function was simulated by means of traffic simulation,and the VISSIM simulation model of the two-way 10-lane highway was established to analyze the impact of the left hard shoulder on the safety of the multi-lane highway under different truck proportions,different input flows and different passenger and freight management schemes.The results show that the left hard shoulder can significantly reduce the lane change frequency and collision rate caused by damaged vehicles in the inside lane,and improve the traffic safety of the road section.At the same time,with the increase of traffic volume,the conflict reduction range follows the law of first increasing and then decreasing.However,when the proportion of trucks is greater than 30% or the traffic volume is greater than 5500veh/h,the increase of conflicts in the inside lane will lead to the reduction of safety benefits of the left hard shoulder.In addition,the safety benefit of the emergency parking function on the left hard shoulder is more affected by the change of the proportion of trucks under the passenger-cargo mixed travel scheme,and by the change of traffic volume under the passenger-cargo separation scheme.While the emergency stop function plays a safety role,the lateral headroom change caused by the left hard shoulder will also affect the driving safety of drivers in the innermost lane.In this paper,driving simulation experiments were carried out,and entropy weight method was used to screen out the significant indicators of the influence of left hard shoulder side clearance changes on drivers’ vision.The results of variance analysis showed that the gradient rate of left hard shoulder had a significant effect on the driver’s speed and lateral offset.Through the analysis of visual indicators and driving behavior indicators,the recommended maximum gradient rate of the left hard shoulder is 1/60.In addition,the safety indexes of the left hard shoulder at the same gradient rate are compared and analyzed.The results show that,compared with the no-shoulder section,the driver’s driving safety is higher in the continuous section with wider lateral headroom,but the existence of the fade in and fade out section will also bring negative effects on the driving safety.Finally,according to the research conclusions of the use of the left hard shoulder safety risks,put forward the corresponding safety management strategy suggestions.The purpose of this study is to deeply explore the impact of left hard shoulder on the traffic safety of multi-lane highways,and provide more accurate reference for the design and use managers,so as to develop a more scientific reconstruction and expansion plan of multi-lane highways and traffic safety management strategy.The results of this study have practical significance to improve the level of highway traffic safety and optimize the traffic structure. |
