The Effects of Speed Measures on Air Pollution and Traffic Safety

The Effects of Speed Measures on Air Pollution and Traffic Safety


W van Beek, Province of Noord-Brabant, NL; H Derriks, KiM Netherlands Institute for Transport Policy Analysis, NL; P Wilbers, SenterNovem, NL; P Morsink, SWOV, NL; L Wismans, P van Beek, Goudappel Coffeng, NL


This paper is on the relation between car speed measures and air pollution and traffic safety. Recently taken speed measures are described. Effects and assessment tools are presented. The paper ends with do?s and don?ts of speed measures.


One of the measures to decrease the NO2 concentration near motorways and to reduce the number of accidents too is to reduce the speed limit from 120 or 100 to 80 km/h. Its effect is well-known in the Netherlands, since it was introduced on the A13 motorway near the Rotterdam district of Overschie in 2002. This measure was accompanied by strict enforcement. Evaluation studies show that the reduced speed limit led to a significant decrease of both NOx emissions and severe traffic accidents. The strictly enforced lower speed limit also caused a more homogeneous traffic flow, and these two factors essentially caused a decrease of air pollution and improved safety. This success, or the ?Miracle of Overschie?, has led to the introduction of similar speed reduction measures on four more location of the Netherlands? motorway network.

It appears however that the effects of the ?Miracle of Overschie? could not be replicated on other locations. Evaluation research has been performed and results of this work will be shown in the paper.

Research question
This research finding has led to more general questions on the effect of travel speed measures on air pollution and traffic safety. Important questions are: will speed reduction always reduce air pollution and traffic safety simultaneously? Is the effect situation dependent, and if so, which situation is most appropriate. Are the effects similar for CO2 emissions? Are the effects similar for highways and other roads? What cost-benefit effects are known? What are the effects of a stricter enforcement? How to reduce traffic speeds? And so on.

Because this topic is important from a environmental point of view and it has a wide scope of questions we propose a paper following this line:

This paper
First a more fundamental introduction is written. In this introduction we explain the expected relation between travel speed and air pollution based on the main research literature, for example, Nilsson (1982, 2004), Copert, etcetera. We will produce general insight in the relation between traffic speed on the one hand and air pollution, CO2 emissions and traffic safety on the other hand. We can give some initial answers to the research questions.

Second we will describe a number of measures on travel speed which, all, have been taken in the Netherlands recently. The next measures and effects will be described:
- The mentioned speed reduction measures with strict enforcement on five locations in the Dutch motorway network. Much research material is available and we will present the most important results;
- Strict enforcement measures without a speed reduction. In addition some other parts of the motorway network are equipped with strict enforcement. The effects on air pollution were studied;
- Improved enforcement by mobile radar systems. From the late nineties on speed enforcement on motorways increased. Research shows a significant effect on speed choice and air pollution
- Speed alert systems in an urban setting. Pilots with intelligent speed adaptation systems are followed by speed alert systems. When breaking the speed limit, drivers are alerted. A pilot with 200 car drivers who regularly drive near schools is performed in 2007 and the result on traffic safety may be shown in the paper;
- Ecodriving aiming at a lower energy use in transport. From 1998 on, SenterNovem promotes an ecodriving behaviour (Het Nieuwe Rijden) and research has showed the effects are on CO2 emissions and traffic safety;
- Drive slow go fast. A new way of designing roads without traffic lights. This measure combines lower speeds with faster travel times. Research was focused on improved safety and air pollution.

The third part of the paper discusses the question of how the effects of measures on travel speeds can be assessed with help of transport models. A short overview of static models, semi dynamic models and dynamic simulation models and their use concerning this matter will be discussed.

In the fourth and final part of the paper the impacts of speed measures will be discussed. We conclude with a clear overview of type of measures and expected failures and successes.


Association for European Transport