Vehicle ownership and fuel optimisation involves consideration of the net present value of alternative options. The NPV is influenced by the tax status of the user and their subjective discount rate. The spread in fuel prices and personal discount rates of private motorists means that weight reduction which was very attractive in Japan and mildly attractive in UK would be uneconomic in US in 1987. Articulated trucks have been studied in detail in Australia.Changes expressed as A$ per 1% reduction in fuel consumpton are uneconomic if their cost exceeds 1.3% of the annual distance. Aerodynamic drag reduction is a profitable design option to reduce the fuel consumption of future cars and trucks.