It has been observed that older high traffic motorways experience lower traffic growth than newer ones (ceteris paribus). This phenomenon is known as traffic maturity in analogy with market maturity, a well known stage ofproducts lifecycle. However, it is not captured through traditional time-series long-term forecasts, due to the constant elasticity to gross domestic product (GDP) that these models assume, leading to traffic overestimation. In this paper it is argued that traffic maturity results from decreasing marginal utility of transport. The elasticity of individual mobility with respect to revenue decreases after a certain level of mobility was reached. In an aggregated approach, it is conducive to decreasing elasticity of traffic demand with respect to economic growth. In order to find evidences of decreasing elasticity we analyse a cross-section time-series sample including 40 sections of French motorways and test for parameter variability. Both analyses show that decreasing elasticity can be observed in the long term. A decreasing function is then proposed for the elasticity of traffic demand with respect to economic growth, which depends on the traffic level on the road. This model seems to well explain the observed traffic evolution and gives a rigorous econometric approach to time-series traffic forecasts. For the covering abstract see ITRD E139491.
Abstract