Estimation of distance headway on two-lane highways using video recording technique

Abstract

Distance headway is the physical separation, in meters, between any pair of successive vehicles in a traffic lane measured from same common feature of the subject vehicles; either rear-to-rear or front-to-front. It is a significant microscopic traffic flow characteristics parameter used in various traffic engineering applications such as level of service, highway capacity analysis, traffic safety and microscopic traffic simulation. Its values are also essential in evaluation of congestion level and overtaking manoeuvre related problems. Distance headway, being spatial parameter is difficult to measure directly in the field. However, it is usually estimated from other parameters; particularly, traffic density, which is also difficult to measure directly but estimated from other parameters based on spot observation. Estimates of distance headways from such approaches may not be real representation of desired values, especially for situations where the parameter is to be evaluated at intervals over a roadway segment. This paper presents a novel approach for direct field measurement of distance headway on two-lane highways using video recording instrumented vehicle. Data for the study were collected from six segments of two-lane highways from Johor, Malaysia. Findings form the study demonstrate that the approach reported herein can be used to measure distance headway directly in the field as against the existing practice of estimating it from other variables based on spot observation despite the fact that it is a spatial parameter.