The Relationship between Capacity and Driver Behaviour

Analytical models use traffic stream capacity as a basic parameter in traffic performance estimation. Traffic characteristics that affect capacity are not often clearly explained or understood. This causes difficulties in practice when professional judgement has to be used in interpreting output and calibrating models for specific applications. There is also a need to establish relationships between traffic parameters used in analytical models and microsimulation models. This paper presents a general analytical model that provides a common formulation relating key variables in intersection analysis to various driver behaviour (driver-vehicle) characteristics. These key variables are follow-up headway for gap-acceptance situations (roundabouts, sign control, and filter turns at signals) and saturation flow rate for signalised intersections. This provides a direct relationship between capacity and parameters representing driver behaviour, namely driver response time during queue discharge, spacing between vehicles in the queue (jam spacing) and saturation (queue discharge) speed.