The dependence of vehicle emission profiles on traffic growth, technology gain, and fleet turnover: A comparative study and sensitivity analysis

In this paper we explore the dependence of vehicle emission profiles over a twenty-five year period on three factors: the rate of traffic growth (g), the fleet renewal rate (λ), and the technology 'gain' (θ) following a step change in emission standards. Using analytic and numerical methods we determine the conditions relating to g, λ, and θ which result in three types of emission profile. These consist of: type-I profiles, in which emissions continue to rise but at a reduced rate; type-II profiles which fall, attain a minimum, and subsequently rise from a lower base; and type-III profiles which continue to fall over a forecasting period. For all profiles we determine the total reduction in vehicle emissions arising from revised standards, and the sensitivity of the total emissions to changes in their determining factors. Data from the UK are used to illustrate the approach which is extended in a wide range of sensitivity tests to explore differences in emission profiles between advanced industrialised and rapidly developing countries. We show that while it may be necessary for all countries to rely on both technological and behavioural policy instruments to reduce emissions, in advanced industrialised countries it may be more effective to improve emission standards, while, in contrast, moderating the rate of traffic growth may be relatively more effective in the rapidly industrialising world. The profiles resulting from the change in emission standards accompanying the introduction of catalytic converters are used to illustrate the general approach.