A Pigovian tax is a tax on market activities that produce some kind of negative externality for society. The basic idea behind the tax is to try and use it to correct something that is happening, but that isn't all that desirable. Examples of negative externalities might include things like pollution and traffic congestion.

Traffic congestion is a bad thing, which is why I have long been a supporter of road pricing. We know how to do this. It has been proven to work in countless cities, including Singapore, London, Stockholm, as well as many others. But in most cases, there isn't the political will. That has certainly been the case here in Toronto.

Maybe this post will help.

A recent study by ETH Zurich, the University of Basel, and ZHAW has looked at the effects of Pigovian pricing on mobility within Switzerland. The study included 3,700 participants and spanned both French and German-speaking parts of the country.

The way the study works is pretty simple. They took thousands of people, gave them a transportation allowance (in Swiss francs), and then assigned costs to the various mobility options. These costs were intended to be commensurate with their amount of negative societal impact.

Driving, for example, came at a cost of 0.1 Swiss francs per kilometer. Whereas participants actually earned money for walking, since you could fairly easily argue that walking produces a net benefit to society. At the end of the four-week experiment, participants were allowed to pocket whatever money was left in their transportation wallet. So in theory there was an incentive to spend less.

What the researchers were trying to do was simulate Pigovian transport pricing and give people a more direct understanding of the societal costs associated with how they move around. And based on their results, it looks to have worked.

What the results show is that when you start pricing transport in this way, all mobility declines slightly (the "all modes" line). But that the biggest hit is, not surprisingly, driving. Car use declined by almost 5%, whereas walking, biking, and using public transit all increased. (The price elasticity of demand for car travel was found to be similar to when the cost of gas increases -- people drive a bit less.)

The authors go on to argue that longer-term Pigovian pricing is likely to produce an even greater impact on mobility, as people would likely adjust and start making bigger decisions about where and how they live. That seems plausible to me.

For a full copy of the study, click here.