Collection and evaluation of projected time gap using CAMDAS

Abstract

Time gap is by far the most widely accepted measure for drivers' gap acceptance behaviours in gap acceptance studies. Nonetheless, time gap, as conventionally measured after a vehicle clears a fixed reference line in an intersection, is sometimes inadequate in representing gap acceptance behaviours, because it is measured well after a driver's decision-making time. Projected time gap (time gap 'projected' to a fixed reference line at the instance when a driver makes the crossing or merging decision), though intuitively a better measure, is beyond the capability of conventional methods. This paper, adopting CAMDAS-a Video Image Processing (VIP) software package - presents a practical approach, which is capable of extracting the distance gaps as well as the associated major-road vehicle approach speeds, and hence the projected time gaps. The relationships between time gap, distance gap, projected time gap and the major-and minor-road vehicle speeds are also established and evaluated.