This article argues that transport problems tend to become worse soon after improvements and partial solutions are introduced. For example, after safety measures are introduced, speed often increases to bring accident rates up towards their previous rates. Vehicle drivers show a similar tendency of risk compensation to maintain a steady level of risk. The serious pollution caused by heavy horse-drawn traffic dropped sharply when motor vehicles replaced it, then air pollution from vehicle exhaust emissions rose, as traffic increased. It is expected to fall then rise again after the introduction of cleaner vehicles with lower emissions because drivers may then travel further. It may never be possible to build enough roads to overcome congestion, because traffic usually rises to exceed road capacity. Braess's paradox states that adding new routes often worsens congestion. With increasing mobility, people tend to move further from city centres, thus have longer journeys; this problem is much worse in the USA than in Europe, and it will be difficult to solve by urban planning. In Trondheim, Norway, road pricing has already shifted modal split towards public transport. All over the world, people who acquire additional wealth use part of it to increase their mobility and speed of travel. For the covering abstract, see IRRD 896880.
Samenvatting