Behavior Mechanism Of Discontinuous Line Markings Adjusting Headway In Car-following

Drivers are the critical determinant in road traffic system.They mainly absorb visual information from the road environment as an assist for its safely driving.There is a great deal of perceptual behaviors of drivers during the obtaining and processing of the visual information.Hereinto,the most fundamental perceptual behaviors are location perception,distance perception,speed perception,and time(to collision)estimation,etc.In this research,a series of controlled experiments of visual information from line markings,was carried out on several high-grade highways of various road and traffic conditions,with naturalistic car-following characteristic data collected,and discovered the phenomenon that the discontinuous line markings adjusted headway in car-following;discerned the temporal and spatial information features of the discontinuous line markings,by introducing the temporal frequency,spatial frequency,and the characteristic elements of car-following behavior;related the complex and hard-to-quantify visual information,from the discontinuous line markings,drivers' visual information perceptions,with car-following behavior,by employing structural equation models;analyzed the behavior mechanism of the temporal and spatial information,from the discontinuous line markings,adjusting headway in car-following;revealed the quantitative and interactive causal relationship among the visual factors,from the discontinuous line markings,drivers' visual information perceptions,risk perceptions,and the headway adjustment behavior in car-following;and comparatively studied the difference of the influence of the discontinuous line markings on headway adjustment behaviors on straight and curved segments of highways.The main contributions of this research are that:(1)Discovered that the discontinuous line markings increased the time headway and distance headway,and decreased the average speed of the test segment;and the increase effect in headways and the decrease effect in speed could be strengthened,when the period of line markings was small or when the temporal frequency was high yet within the interval of [5Hz,14Hz].(2)Discovered that the line markings with horizontal offset or longitudinal gap can lead to ‘discontinuity effect' under the situation of high-speed motion,which caused increase in time headway of car-following;and the horizontal offset can leadto a greater effect of distance headway increase,while the longitudinal gap can lead to a greater effect of speed decrease.(3)Discovered that a bigger installing angle of the line markings,with respect to the moving direction of vehicles,can lead to a greater effect of headway increase and speed decrease;and the reasons was that the drivers' speed perception and distance perception were altered due to Zollner Illusion and linear perspective effect generated from the line markings.(4)Designed a kind of discontinuous line markings with ‘reverse' linear perspective information,and it was found that it can lead to increase in headway in car-following;and there was more significant effect of headway increase when this kind of line markings were installed denser in a unit length of the roadway,because,in which,it produced a stronger effect of ‘reverse' linear perspective.(5)Revealed the interactive causal relationship among the visual factors,from the discontinuous line markings,visual perception variables,and the headway adjustment behavior in car-following,by employing structural equation models.And the models indicated that,1)the normalized influence coefficients between the installing angle,leading vehicle size,temporal frequency,collision index,and the distance headway adjustment behavior in car-following,were 0.22,0.35,0.18,and0.25,respectively;the normalized influence coefficients between the longitudinal gap,horizontal offset,initial headway,temporal frequency,and the time headway adjustment behavior in car-following,were 0.24,0.23,0.13,0.24,and 0.16,respectively;2)as compared with the risk perception of collision,the risk perception of distance can lead to a greater effect of distance headway increase,since it can produce a stronger feedback of car-following safety to drivers;3)the direct and indirect rear-end risk can affect the time headway and deceleration in car-following cooperatively,while the direct rear-end risk perception,dominated by perceived distance factors,can lead to a more significant effect of time headway increase.(6)After installing the discontinuous line markings on the roadways,the time headway distribution of car-following tend to be concentrated on straight segments,and the time headway was significantly increased on curved segment.(7)This research can reduce the rear-end collisions on highways by optimal designing visual information on road surface,and it could provide a scientific novel thought and a low-cost novel method to level up the road traffic safety.