Proportion of vehicles moving freely depending on traffic volume and proportion of trucks and buses

Tomasz Szczuraszek,Elżbieta Macioszek

doi:10.3846/bjrbe.2013.17

Abstract

Adequate description of traffic in all intersections where traffic is not controlled by traffic lights is substantially affected by the adopted model of proportion of vehicles which move freely in traffic flow. The present study attempts to evaluate the proportion of vehicles moving freely in traffic flow depending on traffic volume and the effect of proportion of trucks and buses on this parameter. The analyses were carried out with an example of flows of vehicles moving in small roundabouts. It was observed based on the results of the analyses that the proportion of vehicles moving freely in traffic flow depending on traffic volume is best characterized by a spline, composed of three components which include quasifree traffic, uniform traffic and non-uniform traffic.

Highlights

One of the most important characteristics which describe the traffic flow, essential from the practical standpoint, is headway between vehicles
The present study attempts to evaluate the proportion of vehicles which move freely in traffic flow depending on traffic volume, i.e. function φ(Q) and the effect of trucks and buses on this function
The adequateness of the description of traffic in all the intersections where traffic is not controlled by means of traffic lights is strongly dependent on the adopted model of the proportion of vehicles which move freely in traffic flow

Summary

Introduction

One of the most important characteristics which describe the traffic flow, essential from the practical standpoint, is headway between vehicles. The present study attempts to evaluate the proportion of vehicles which move freely in traffic flow depending on traffic volume, i.e. function φ(Q) and the effect of trucks and buses on this function These analyses were carried out with an example of vehicle flows which move on small roundabouts. The quality of adaptation of root function to the empirical data which describes the dependency of the proportion of vehicles which move freely on traffic volume on a roadway of small roundabout in the third range of variability Q was assessed based on the evaluation of absolute errors δC (%) for individual measurements using the following dependency: δC φiM − φiE φiE. In consideration of the results of the analyses presented, one can note that even insignificant proportion of trucks and buses in traffic flow causes substantial decline in the number of vehicles which move freely in individual classes of traffic volume. High conformance of the profile of the function φ(Q) with the models developed by the authors of this study is observed for the Tanner’s model (Eq (6)) and partially (for Q > 300 vph) for Hagring’s model (Eq (8))

Many of the previous models raise some doubts about their adequateness:

Findings

Conclusions