Research On Expressway Driving Safety Considering Coupling Effects Of Vehicle Features And Geometric Alignments

Expressway mileage and holdings of vehicle in our country have been continuously increasing for the past decades.As such,efficiency of traveling and freight boosts at an advanced rate.It should be noted that expressway accidents,compared with the developed countries,are still an unsolvable issue in China in spite of continuingly dwindling.As an integrated system of driver,vehicle,roadway,and environment,expressway safety are influenced by multiple factors.There are 3 principle problems with current researches on expressway safety,including,1)insufficient consideration of most unfavorable vehicles,in terms of inadequate researches on buses and trucks and outdated vehicular information,2)discrete considerations of geometric alignments which cannot accurately characterize expressway as it is three-dimensionally stretch and superposition,and 3)few researches on quantifying sensitivity of vehicular traveling status to geometric alignments.This research is in an attempt to quantify relationship and analyze sensitivity of vehicular traveling performance to three dimensional geometric alignments of expressway by vehicular dynamics simulation method.In this study,vehicles were classified into passenger cars,buses,and trucks.Vehicular features of the three types,including three dimensional size(i.e.,length,width,height,and wheel base),dynamic parameters,vehicular body,and suspension types,were extracted from online vehicular database.By analyzing the extracted vehicular data,features of the most unfavorable vehicle of each type were fixed.And vehicle simulation models of each type were constructed in vehicular simulation platform based on the most unfavorable features.Load characteristics have been proven to be influential to dynamic performance of buses and trucks.Hence,models of buses and trucks with different loads were separately constructed by modifying the mass of subsystem of the model.Load characteristics included empty load,1/4 loads,1/2 loads,3/4 loads,and full loads.And coupling model of vehicles and expressways was established by integrating expressway model with different geometric alignments with the vehicular model.Vehicular dynamic indices,including Load Transferring Rate(LTR),Lateral Coefficient(μ),and different of velocity between cars and trucks,were selected to evaluate vehicular traveling status.Three dimensional geometric alignments included horizontal tagent length,horizontal radius,vertical grade,and grade length.Relationship between vehicular traveling performance and three dimensional geometric alignments was quantified.Results showed that different types and load characteristics of vehicles had different performance.Based on the established relationship,sensitivity of vehicular traveling performance was analyzing by marginal effects principles.Results showed that different types of vehicles were sensitive to different geometric alignments.The established relationship was testified by collected field data.The data was collected on East Mountain Lu segment,Changshen Expressway(G25).Moreover,traffic accident data on the rural interstate highway(expressway in China)was analyzed.Relationship between accident frequency on segment and geometric alignments of segment were quantified by Seemingly Unrelated Negative Binomial(SUNB)model.Results showed that the selected vehicular dynamic indices could accurately simulate vehicular operations on the real expressway segment.Compared with existing studies,our study has three prime innovational points: 1)vehicular model in our study is more close to real traffic and updated,as they were established based on extracted vehicular features and considered different load features;2)geometric alignments were studied three dimensionally in our research,also vehicular type and load features were considered as they have coupling effects with geometric alignments;3)sensitivity of vehicular traveling performance to three dimensional geometric alignments was quantified in this study,equipping expressway designers a reliable comparison benchmark when conducting expressway design.