Abstract
One type of gravity model for describing the distribution of journeys from zone to zone in a town requires the introduction into the equation of two normalizing factors for each zone. This is in order to satisfy the conditions that the sum of the number of journeys from or to a zone is equal to the number of trip-ends known to be there. This article demonstrates a theoretical interpretation of these normalizing factors, which are shown to be approximately equal to a function of the mean journey cost. This leads to an approximate non-iterative method of estimating the parameters of a deterrent function. Other implications of the interpretation are also drawn.