This paper presents a simple model which describes the way in which a bus service network is able to serve its passengers in a large area of constant uniform travel demand. The model determines the generalised cost of travel to the passenger in terms of time spent walking, waiting and travelling, and the bus fare, which will depend upon the cost of providing the given level of service. The service network is adjusted to provide an 'optimum' service (i.e. that which minimises the total generalised cost of travel, but without any consideration of generated or suppressed trips) in terms of the average spacing between routes, the average density of buses per unit area, and the average spacing of bus stops. Optimisation is also considered for the case where travel demand can be described in terms of a constant off-peak level of demand, and another constant level of demand during the peak periods, in a situation where the cost of providing a bus in the peak is greater than the cost of an off-peak bus, the difference in cost depending on the relative numbers of buses in service in the peak and off-peak. The model is calibrated against data for both central London and central Glasgow, and the optimum route parameters suggested by the model are seen to be in reasonable agreement with present practice in both cases. (Author/publisher)
Samenvatting