Traffic Safety Control Theory And Technical Countermeasures Of Expressway In Fog Areas

The mountainous expressway corridor is easy to form relatively fixed fog areas due to the small regional environment.The limited visible space is very unfavorable for safe driving,and the serial rear-end collision is mainly type of traffic accident that often embraces high mortality and negative social impact.At present,there are shortcomings such as the general quantitative evaluation of the speed limit schemes and the standard of the vehicle distance control,moreover,the selection and layout of the traffic safety facilities mostly rely on experience.The richness of the theory and the security system in the fog areas are in favor of the realization of a more reasonable,effective and low-cost set of driving safety measures.The paper firstly clarifies the general characteristics of the fog areas and analyzes the accident characteristics and causes,meanwhile the relationship between the meteorological optical range and the visible distance is studied.Secondly,the free flow speed under different fog conditions is determined by the stopping sight distance and the theoretical recommended speed limit under different fog conditions and different traffic volumes is obtained by the flowspeed curve based on the M/M/1 queuing theory.Then the speed limit schemes of the Standard for expressway traffic safety control under fog weather conditions(GB/T 31445-2015)is optimized.Taking the speed limit value at 150m/250 m visibility as an example when the visibility is greater than 100m(the adjacent lane speed difference is greater than or equal to 15km/h),the speed limit schemes for different lanes,types of vehicles and combining the two are respectively simulated at medium and low traffic levels based on 4-lane expressway by VISSIM which the ratio of HGV is set to 10%,20%,30%,40%.The cross-sectional traffic volume,travel time of car,M_BND and compliance rate of MSDE are selected to evaluate speed limit schemes by weighted Topsis comprehensive evaluation method based on AHP.When the visibility is less than or equal to 100 m and the traffic volume is greater than 2500vph~3000vph,the vehicle restriction can be taken according to the variation trend of the safe MSDE mean and vehicle conflict rate with traffic volume which is derived from simulating vehicle restriction at 6 different traffic levels.Finally,a simplified vehicle braking distance model is stablished which is verified by Carsim/Trucksim under different speed and braking system pressure.Depending on it,the safety distance model is constructed and the safety distance control standard of the fog areas is obtained.According to the 2015~2017 visibility data(value and frequency)of Yunnan Yibi expressway,the 9 fog areas along the line are divided into 5 levels.Induction sign and visual guidance facility have been developed in the 1/2/3/4 response fog zone,further more,the traffic safety control measures for the fog area of Yibi expressway are proposed based on real-time visibility and traffic safety linkage control system is initially established for fog areas.The results provide support for the operational safety of the Yibi expressway in fog areas,enriching the related safety control theory and technology system.