Vehicle Fleet Dynamics

Thoresen, T. R. L. and M. R. Wigan (1980). Vehicle population dynamics: tracing, forecasting, and assessing changing population characteristics. 10th Australian Road Research Board Conference, Sydney, Australian Road Research Board, Vermont, Victoria.

A significant number of road transport study areas including road project evaluation, aggregate automotive fuel consumption measurement, road user charging strategies, and road safety require access not only to detailed descriptions of particular vehicle fleets but also to changes in these over time. A survey of the available data and literature indicates, with some exceptions, that data deficiencies are encountered in both population profiling and tracing change, and that the need to trace change has been inadequately appreciated. Rectification of the latter is required to set individual studies in context, and to improve results notably where assumptions relating to future vehicle populations, composition and usage are employed.  A methodology interrelating the various particular target vehicle populations employed in studies, such as fleets on register, fleets 'on the road', and fleets used or accessible to economic entities is advanced, and a number of methods of measuring change together with associated data requirements put forward. While restricted primarily to use of private vehicles in urban areas, the results were found to be encouraging. Significant change in vehicle characteristics was indicated. Results yielded by surveys of differing target populations proved compatible, supporting the methodology advances, and projections of population age distributions based on prior estimates of vehicle life expectancy proved to be an effective means of detecting and forecasting change at a macro level. A need for a standardised method of characterising vehicles was also identified to facilitate inter population comparisons and maximise use of available data.  In view of the results achieved, further work is recommended to trace, forecast, and explain changing vehicle populations and their usage, plus some extension of these analyses to non urban areas and freight.  The collection and appropriate use of vehicle operating costs is a major area for the early application of the methodology proposed

Thoresen, T. R. L. and M. R. Wigan (1985). Fleet dynamics: Australian motor car fleet population adjustments over a decade of significant change. 13th Australian Transport Research Forum (ATRF), Melbourne, Victoria, Australian Road Research Board.

Despite stagnation in sales of new vehicles since the mid nineteen seventies, both the size and total usage made of the domestic population of cars and station wagons continued to grow unabated.  This paper looks at the factors behind this apparent contradiction, as well as attempting to assess whether the 'downsizing' phenomena observed overseas was reflected by the Australian experience. It was found that the prime causes of continued vehicle population growth were increased vehicle life expectancy and a favourable (ie young) initial population age structure.  Growth in total vehicle usage was found to reflect higher utilisation of light/ medium vehicles over their operating lifetime. Available tare mass data indicated no clear trends with respect to 'downsizing'. Examination of motor vehicle census data indicates that while there was a shift away from vehicles in the heaviest tare classes this was matched by a similar decline in relative numbers of vehicles in lightest tare categories. A small reduction in fleet average tare will result if current new registration patterns persist. Analysis of the stock adjustment process indicates that while the growth rate of the total population would decrease in the event of a continuation of current vehicle market conditions, stagnation is unlikely in the immediate future

Thoresen, T. R. L. and M. R. Wigan (1988). "Australian private-vehicle fleet changes on register and on road, 1971-1982." Transportation Research A 22(1): 1-11.

Despite stagnation in new vehicle sales from the mid 1970s, both the size and total usage made of the Australian stock of cars and station wagons continued to grow unabated into the early 1980s.  Such apparently contradictory trends were an international phenomena, as were increased sourcing of vehicles from Japanese manufacturers, and the experience of less than favourable economic and demographic conditions.  This paper looks at the factors behind the movements noted, and attempts to assess to what extent the 'downsizing' phenomena observed overseas was encountered in Australia. Increasing vehicle life expectancy and an initially favourable age structure were found to account for contradictory growth rates in new registrations and the vehicle stock, while increased lifetime utilisation of light/ medium vehicles accounted for much of the increase observed in total distance travelled.  Only a weak downsizing trend was detected commencing circa 1979, its weakness reflecting an unexpected trend away from light vehicles. Projections indicate that if levels of, and size patterns associated with, new vehicle registrations persist, downsizing trends will continue to be weak, and overall stock growth rates are likely to slow, although stagnation is unlikely by 1990

Updated and edited on 22 June 2015