EFFECTS OF MOTORWAY SPEED LIMITS ON FUEL CONSUMPTION AND EMISSIONS

Fuel consumption and the emission of air-polluting substances depend o n the driving speed of a car. On 1 May 1988 a system of differentiated speed limits for passenger cars and light-duty vehicles on motorways was introduced in the Netherlands, among other things for the purpose of reducing environmental pollution. On particular sections of the Dut ch motorways a limit of 100 km/h is now in force, on others 120 km/h. The fuel consumption and the CO, NO(x), CO2 and hydrocarbon emissions from passenger cars and lorries on motorways were calculated based on the actual driving speeds on both types of road before and after the i ntroduction of the new speed limits. The emission behaviour at differe nt vehicle speeds was derived from an emission and fuel consumption mo del based on data from field tests on chassis dynamometer test stands in combination with measurements under actual driving conditions. Shor tly after the introduction of the new speed limits the average driving speed decreased sharply, resulting in lower fuel consumption and emis sions. In spite of intensive information campaigns and a sharpened enf orcement policy, the average speeds have gradually increased since, wi th the result that benefits have already largely disappeared. The intr oduction of less polluting cars and the growth of motorised traffic ar e the dominating factors for change in fuel consumption and emissions on motorways.