Luc Wismans obtained his doctorate at the University of Twente on 27 September on a research project into optimizing traffic flows. His conclusions? Holding back traffic at certain points is generally an effective strategy for meeting several policy objectives. Tackling problems relating to accessibility, air quality and climate can easily be combined, but only at the expense of traffic safety and noise nuisance. Improvements are certainly possible in comparison to the current situation, but it is up to politicians to make the necessary courageous decisions.
Luc Wismans, a researcher at mobility consultants Goudappel Coffeng, and a PhD candidate at the University of Twente, carried out research into optimization strategies for dynamic traffic management: dispersing traffic over multiple different roads by programming traffic lights and using variable speed limits. Specifically, his research concerned the question of how various policy objectives relating to sustainability were interconnected. In other words, is it the case that what is beneficial to for traffic flow, for example, could be detrimental to traffic safety? Is a higher speed limit on a particular stretch of road always bad for the environment? Wismans looked at travelling times, fine particles, noise nuisance, CO2 emissions and traffic accidents.
Making choices
Journey times and emissions appear to be less diametrically opposed than frequently thought. Wismans examined traffic behaviour in a certain area. If as many people as possible can keep moving constantly, then that benefits both the average journey times and the objectives relating to the emission of harmful gases. It is therefore about preventing traffic queues, especially in urban areas. It appears that there is always a degree of conflict between the various objectives. With regard to noise, it is desirable to keep a check on speed, for example, while as far as road safety is concerned, it is important to keep traffic on motorways, which are relatively safe, for as long as possible. Wismans says, “This really does need to be seriously considered by politicians. What is more important to us? Current practice is chiefly about optimizing journey times – as far as the environmental impact is concerned, any action taken goes no further than carrying out measures to see if the results fall within the set norms. I have devised a range of instruments with which all policy objectives can be assessed in the optimization process.”
Higher speed can also be good for the environment
Wismans’ second conclusion relates to the effectiveness of ‘dosing’ – preventing vehicles from joining certain traffic routes or encouraging the use of particular routes. He believes there are considerable benefits that could still be gained in the Netherlands through the careful selection of ‘dosing’ points. Wismans explains, “Dosing seems to be a generically applicable strategy for reducing the negative secondary effects of traffic. It is not necessarily true that lowering the speed limit is better for air quality, for example. I have looked at the effect across the whole area. If traffic is moving more slowly on a ring road, you may get more rat-running through the city, for example. The environmental plus on the ring road actually turns out to be an environmental minus. Unfortunately, current practice often involves looking at things selectively.”
About the research
Wismans developed his instruments at Goudappel Coffeng, the market leader in the field of mobility, traffic, public spaces, and the environment. He analysed both a fictitious road network and a representative section of roads around Almelo. Wismans conducted his PhD research at the Centre for Transport Studies (CTS) of the University of Twente. His thesis supervisor is Professor Eric C. van Berkum.
