This report describes the basic structure and mechanism of the traffic assignment model CONTRAM. The description is relevant for all versions of CONTRAM: recent developments in the modelling in CONTRAM version 5 are listed briefly. An iterative procedure is used to assign vehicles to their minimum journey time routes through a network taking into account the delay at each junction along a route at the time that a vehicle reaches each junction. The assignment procedure, which uses a packet structure to represent elements of flow of vehicles for movements between Origins and Destinations, allows multi-routeing for vehicles with freedom of choice of route; fixed route vehicles, such as bases, are sent along their predefined routes, but still encounter the same delays at junctions experienced by other vehicles. The modelling in CONTRAM is consistent with the queue calculations in ARCADY, PICADY and OSCADY. Facilities allow for: a full range of junction types; three classes of vehicle; blocking-back between junctions; three options for inputting signal data; fixed route vehicles (eg buses); fuel consumption; banned vehicle movements (without recoding) and 'point-to-point' speeds for comparisons of speeds for selected O-D movements. Recent developments in CONTRAM 5 include speed/flow relationships for links, minimum behavioural (or perceived) cost assignment, a more detailed modelling of the effect of linked signals, an improved fuel consumption model, estimation of geometric delay at junctions, a condensed output file for post analysis work, variable and automatic packet sizing, variable saturation flows and capacities for individual time intervals.

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