Computer user manual for program LATM (version 4.1) : a program package for local area traffic modelling

This manual provides the necessary documentation for the use of the LATM traffic model on mainframe computer systems. The package produces short duration traffic assignments for small area networks representing part of an urban area. It can be used for the evaluation of alternative traffic systems management schemes, studies of traffic generators such as shopping centres, or studies of congestion and network performance. The package uses externally supplied, dynamic travel demands over a specified time interval (e.G. A peak hour) which is itself divided into a number of computation subintervals. Demand is assumed to be constant in each subinterval, but may vary between subintervals. Network travel conditions are also varied between subintervals. It is possible to distinguish between different turning manoeuvres at intersections, between intersection types, and between road and street types. Queues may exist on all intersection approaches. The model uses a probabilistic path choice procedure based on perceived travel times to account for the possible multiplicity of available network paths of comparable travel time and the assumed imperfect knowledge of the network by travellers. No limits on network size, number of computation subintervals or interval length are set in the program. However, the queuing capacity and delay submodels in the package are not appropriate for subintervals of less than 5 minutes. A non consistent set of metric units is used. The model has flexibility to be used at varying degrees of detail of the network description.