Cause Analysis And Mitigation Strategy Research Of Recurring Traffic Congestion In Interchange Section Of Suburban Expressway

Suburban highway interchanges,vital facilities for traffic transition within road networks,have garnered widespread attention due to their chronic congestion adversely impacting residents’ mobility in recent years.Scholars have explored the congestion mechanisms in highway interchange areas,identifying key factors contributing to congestion.However,the complex nature of highway traffic systems has prevented researchers from determining the interrelationships among internal generative congestion factors,and the multidimensional,structured,comprehensive impact mechanism still needs to be determined.This paper,focusing on the typical characteristics of suburban highways,employs Qualitative Comparative Analysis(QCA),Partial Least Squares Structural Equation Modeling(PLS-SEM),and traffic simulation based on traffic data and field measurements to delve into the causal mechanisms of congestion in suburban highway interchange areas and propose corresponding congestion alleviation techniques.Grounded in traffic data from 17 observation stations on Xi’an’s ring highway in recent years,this study investigates design flaws contributing to the chronic congestion of suburban highways.By examining the overall distribution,peak distribution,daily variation,and temporal variation of annual hourly traffic volume on suburban highways,it is revealed that under the backdrop of the tourism economy,people’s travel patterns have significantly changed,and the design hourly traffic volume and peak hourly traffic volume coefficients affecting road capacity are severely misaligned with current travel characteristics.Research findings indicate that the recommended hourly traffic volume coefficients in existing standards are approximately 25% lower than the actual design coefficients,leading to over 200 hours of traffic congestion annually when using the recommended values for the geometric design of highways,far exceeding the anticipated 30 hours.These results reveal design flaws that contribute to frequent congestion on suburban highways.Based on traffic data from observation stations and field measurements,this study examines the impact of traffic flow characteristics and environmental factors on congestion in the diverging area of suburban highways.Given the limitations of statistical analysis methods based on linear causal relationships in effectively addressing complex congestion issues,the QCA method is employed with traffic volume,heavy vehicle intrusion rate,diversion traffic ratio,forced lane-changing instances within the diversion area,and weather as causal variables to systematically investigate potential relationship combinations between congestion causation and internal generative factors in suburban highway exit sections,identifying four condition configurations that lead to congestion.To further clarify the quantitative impact of these multivariate concurrent combinations on congestion,PLS-SEM is used to establish a structural equation model of the concurrent influences of multiple factors in interchange diversion areas based on condition configurations,yielding normalized weights for the impact of individual factors on congestion.The study reveals that forced lane-changing instances within the diversion area,heavy vehicle intrusion rate,and traffic volume have normalized weights of0.389,0.225,and 0.141,respectively,indicating that forced lane-changing behavior within the diversion area is the most critical factor in the formation of congestion in the area.The findings offer novel insights into the complex causal relationships underlying congestion at exit sections.Forced lane-changing instances within the diversion area represent the most crucial driver behavior factor triggering congestion.To determine the distribution characteristics and influencing mechanisms of forced lane-changing locations,this paper explores the relationship between forced lane-changing locations and guide sign information volume.The relationships between driver physiological responses,cognitive load,and sign information volume are analyzed through simulated driving experiments and the relationship between forced lanechanging locations and driver physiological responses and cognitive load.The study identifies differences in information acquisition effectiveness and distribution characteristics of forced lane-changing location choices under varying sign information volumes.Results demonstrate that guide sign information volume significantly impacts the distribution of driver lanechanging location choices,with larger information volumes leading to lane changes closer to the exit and more forced lane-changing instances within the diversion area.To alleviate traffic congestion,the information volume of exit guide signs should be at most 11 information units.Additionally,the macroscopic impact of traffic flow characteristics on forced lane-changing location choices is analyzed based on field measurements.Results indicate that the relationship between traffic volume and the number of forced lane changes within the diversion area is Ushaped,and both heavy vehicle intrusion rate and diversion traffic ratio exhibit positive correlations with the number of forced lane changes within the diversion area.The study examines the impact of traffic flow characteristics and environmental factors on congestion in the merging area of suburban highways.Through in-depth analysis of field observation data,it is found that drivers commonly engage in early merging behavior,i.e.,merging onto the mainline without fully utilizing the acceleration lane,which is a significant triggering factor for traffic congestion.The QCA method is used to identify sufficient and necessary condition configurations for congestion occurrence.Consistency and coverage scores reveal that high mainline traffic volume,high merging traffic volume configurations,and high heavy vehicle intrusion rate and high merging traffic volume configurations can be considered sufficient conditions for congestion in merging areas.Among them,high merging traffic volume conditions have consistency and coverage scores of 0.94 and 0.85,respectively,indicating that a large merging traffic volume is a critical factor for congestion in merging areas.Using VISSIM to simulate traffic congestion in merging sections,the study incorporates mainline traffic volume,merging traffic volume,heavy vehicle intrusion rate,and early merging behavior,and establishes an interrelationship model for these factors under critical congestion conditions through curve fitting.This model can predict the maximum allowable merging traffic volume without causing congestion in merging sections based on mainline traffic volume and heavy vehicle intrusion rate,providing theoretical support for traffic volume regulation at the network level during peak hours.Based on the findings above,congestion mitigation strategies and techniques are proposed from design,macroscopic traffic control,and microscopic traffic guidance perspectives.To address design flaws,a new design hourly traffic volume index for suburban highways is proposed,suggesting the continued use of the 30 th highest peak hourly traffic volume in areas where land and economic conditions permit,with a suitably increased design hourly traffic volume coefficient.Without observational data,the design hourly traffic volume coefficient should range between 11.5% and 12.5%.If conditions are constrained,the 80 th highest hourly traffic volume can be adopted,with a design hourly traffic volume coefficient between 10.5%and 11%.Regional and microscopic traffic organization techniques are proposed based on the critical factors and condition configurations for congestion occurrence in diverging and merging sections.This paper identifies the road design flaws contributing to congestion in suburban highway interchange areas,clarifies the possible relationship combinations between congestion causation and internal generative factors in suburban highway interchanges,and proposes corresponding traffic congestion alleviation techniques.These findings provide a theoretical foundation and new perspectives for understanding the complex causal relationships underlying congestion at exit sections and hold significant implications for scientifically addressing suburban highway traffic congestion.