In the political discussion relating to transportation policy, surprisingly little attention is paid to the increase in distance travelled as a result of improved infrastructure. For passenger transport empirical data indicate that the speed elasticity of mileage demand is approximately 1. This means that the distances travelled increase proportionally to the travel speed. Using elasticity functions that are well known from economics, we derive a general formula to calculate traffic induced by the improvement of infrastructure. The realistic consideration of induced traffic is a precondition for the assessment of environmental effects (fuel consumption and emissions). Acceleration of traffic by improved infrastructure is identified as a major reason for traffic growth. The most efficient means of transportation demand management is to decelerate traffic. We derive how fuel consumption and emissions are to be calculated for arbitrary numerical values of the speed elasticity. (A)
Abstract