Approximation of time headway of two-lane highways using test car approach

Abstract

Time headway is an essential variable in various traffic engineering applications such as capacity and level of service analyses in numerous contexts which include road sections, roundabouts, merging manoeuvres, priority junctions, and so on. In relation to level of service analysis of road segments, the proportion of traffic traveling with headways less than 3 seconds at a particular point is used as a criterion for assessing the operational performance of two-lane highways. Generally, headways are measured based on spot observation as the time interval between any pair of consecutive vehicles passing a common point of a road. Spot measurement has been identified as the major problem with collection of headway data as the approach does not consider the variation of the headways along the road segment. Hence, this necessitates the need for developing other techniques for estimating headway along road section as opposed the current practice of spot measurement and deemed applicable for longer segment. This paper presents a different approach for measurement of time headway based on space observation using test vehicle method. Field data on time headways were collected on two-lane highways using both spot and space observations and the results compared. Statistical analysis using t-test indicates that the two data sets do not differ significantly.