An important element in forecasts of future growth of road traffic is the future level of car ownership. In order to provide a better understanding of the factors which influence it, a number of statistical analyses of past data have been made. These include studies of current levels of ownership in different areas, comparisons of growth rates in different areas and studies of long-term growth patterns. They cover data from britain, the united states and a number of other countries. The effects of a number of factors, including incomes and population densities, have been identified. Over-riding these effects is a strong tendency for the annual percentage growth rates of car ownership to reduce as the level of ownership rises. The logistic curve model used in previous work is shown not to be sufficiently general; an alternative algebraic form is proposed which helps to reconcile an apparent inconsistency between the recent rapid slowing down of growth in britain and other evidence that suggests that saturation is still some way off. A range of forecasts of numbers of cars is made on the basis of the new model and of alternative assumptions about future levels of economic growth and of fuel prices. With the middle assumptions, the new forecasts are somewhat lower than those issued previously, at least up to 1985. Thereafter they may be higher or lower, depending on the saturation level chosen. (Author/publisher)
Abstract