AN EXPONENTIAL RELATIONSHIP FOR THE PROPORTION OF FREE VEHICLES ON ARTERIAL ROADS

The proportion of free vehicles on a road link is dependent on the geo metry of the road link and the presence of intersections along the lin k. This paper details the investigation of the proportion of free vehi cles as a function of the link geometry. It is necessary to define the effects of the link geometry before the effect of intersections on th e headway distribution can be incorporated. Current methods for descri bing the proportion of free vehicles on a road link predominantly use linear relationships with the vehicle dow rate. An exponential relatio nship has been examined and found to be better suited to the modelling of the proportion of free vehicles than the existing linear relations hips. In modelling the flow in each lane, the characteristics of the t raffic flow were found to be dependent on the lane type being modelled . The kerb lane sustained a higher proportion of free vehicles than th e median lane for similar dow rates. This finding is significant in th e analysis of priority intersections. The difference is attributed to driver behaviour and is related to the expected ease of overtaking. Us ing these results the proportion of free vehicles is described as a fu nction of the lane type, lane width and the vehicle dow rate through t he use of exponential relationships. The influence of intersections up on the characteristics of the traffic flow can then be incorporated by describing the effect of the proportion of free vehicles on the road link. Copyright (C) 1997 Elsevier Science Ltd.