Charging people for traffic costs really does cut car use

People who end up paying out of their own pocket for the costs traffic loads onto the community tend to use the car less. That is the finding of an experiment run by the University of Basel with around 3600 people in German-speaking and French-speaking Switzerland, whose results have been published in the journal Review of Economic Studies.

The costs in question do not appear on the receipt at the petrol pump. They are the health damage caused by air pollution and noise, the medical care that follows road accidents, the economic losses tied to time spent in traffic jams and the damage caused by climate change. They are borne by the population as a whole, including people who never get into a car.

The university set out to find whether it is possible to influence road users' behaviour and so reduce the burden that falls on everyone. For eight weeks the participants recorded their journeys through a smartphone application. After the first four weeks the researchers divided them into three groups.

The first group received only an overview of its own mobility habits. The second was told what external costs the journeys it had just recorded generated. For the third, those same costs were deducted from a personal budget, and at the end of the experiment participants could keep whatever was left.

Information on its own is not enough

The clearest result concerns the first two groups. «Simply providing information about the costs did not, in most cases, produce significant changes in habits», the university sums up. Knowing how much one's daily journey weighs, in other words, was not enough to change it.

The effect on the third group was different. When the amount was actually taken from a sum of money meant for them, participants reduced their car journeys and made greater use of other means of transport.

The comparison between the three groups bears directly on awareness campaigns, which rest on information. And it shifts attention to those who carry these costs today without having chosen them. The study does not address how such a mechanism might work outside an experiment, nor which groups it would affect first.