LATERAL ANALYSIS OF LONGITUDINAL HEADWAYS IN TRAFFIC FLOW

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-b ased. These are true only when lane discipline is e xtremely ideal and lane widths are large. Real traffic, howe ver, 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 c ertain value of same-lane time headways, fewer numb ers of drivers were willing to keep short headways with re spect to the neighbouring lane vehicles. This may m ean that, except light flow traffic where the offside lane is primarily used for overtaking, drivers prefer to p ass or lag behind the vehicle in the adjacent lane, rather than drivi ng side by side. In addition to its safety concerns , especially in relatively narrow lanes, this issue may have capaci ty implications. Hence, existing traffic flow model s may require further adjustments.