Abstract:

Mainstream car following theories have assumed that each vehicle is influenced directly by the one in front and vehicular headways have been studied as same-lane-based. These are true only when lane discipline is extremely ideal and lane widths are large. Real traffic, however, poses a more complex picture. The paper, based on empirical observations, attempted to explore the issue of two-dimensional headway analysis in detail for better realism in traffic flow modelling. It was found that below a certain value of same-lane time headways, fewer numbers of drivers were willing to keep short headways with respect to the neighbouring lane vehicles. This may mean that, except light flow traffic where the offside lane is primarily used for overtaking, drivers prefer to pass or lag behind the vehicle in the adjacent lane, rather than driving side by side. In addition to its safety concerns, especially in relatively narrow lanes, this issue may have capacity implications. Hence, existing traffic flow models may require further adjustments

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