|
Abstract
|
In this paper we investigate some implications of including intergenerational fairness when appraising the impact of transport policy on an urban land-use and transport system. The paper also reports on the implementation of an appraisal framework where the main elements of sustainability is taken into account. The land-use and transport system of Stockholm is modelled using the land-use model IMREL, paired with the state-of-the-art transport model SAMPERS.
The intergenerational fairness is handled by modifying the normal exponential discounting of a cost-benefit analysis. We form the weighted sum of a normal cost-benefit analysis and the horizon year costs and benefits without discounting. The relative weight put on each term is governed by an intergenerational parameter, α. What we do is let the undiscounted horizon year represent the long term future, so setting α = 0 means using an ordinary exponential discount rate. α = 1 on the other hand puts all weight on the long term future, ignoring costs and benefits for the years up to the horizon year. We experiment with some values of the intergenerational parameter to see how it affects the ranking of combinations of two policy instruments.
Optimisation is employed to further analyse the implications of using combinations of instruments. A problem that arises when packaging instruments into strategies is that the number of possible combinations gets large. Optimisation can be of use to find the interesting ones. Our modelling package is fairly detailed, which means long computations, and generally not suited for automated optimisation. Instead we use a response surface method, where the objective function is approximated with a quadratic function, which is fitted to model computed values of the objective function by regression. |