A major argument put forward by opponents of highway funding, on which the Swiss will vote on November 24, is that increasing capacity will lead to a shift from rail to road. This is true, but it does not mean that the project is a waste, as congestion will ultimately be reduced. If future population growth puts more pressure on the infrastructure, not adapting it would exacerbate the problem.
The reaction of commuters to congestion
Let's take a simple analytical framework to analyse the choice between car and train, focusing on congestion. The more people use a means of transport, the greater the congestion. The figure below illustrates the resulting choice. We consider a total commuting population of 10 people (the figures are purely illustrative), represented on the horizontal axis. The number of people using cars is read from left to right, and the number using the train is read from right to left. The vertical axis shows the cost of congestion for the car (red line) and the train (blue line).
On the left-hand side of the graph, few people use cars. The roads are not congested, but the trains are packed. This greater congestion on the railways is indicated by a higher value on the blue line than on the red line. Conversely, on the right-hand side of the graph, most people use their car and congestion is greater on the roads than on the train.
Commuters take congestion into account in their choice. The equilibrium point is then in the middle (point A) where the cost of congestion is equalised between the two modes of transport. Being to the left of point A is not an equilibrium, because people will stop taking the train to use their car (and the same goes the other way around).
Impact of road investment
Investment in roads reduces congestion for a given number of users. The impact is illustrated in the following figure, with the red road congestion line moving downwards (from the dotted line to the solid line). If commuters don't change their behaviour, we move to point B where the people on the road are happy, and those in the tain face unchanged congestion.
But this is not an equilibrium, because people adapt and some give up taking the train. The new balance is at point C, where the blue line crosses the new red line. There is a modal shift, as the number of cars has increased. The opponents' point is therefore entirely valid, but they fail to point out that in the new situation the cost of congestion is lower than it was initially. The shift does not imply that the investment is useless, but simply that its benefit also goes to the people still taking the train.
Population increase
An additional point against the proposed project is that, in any case, road congestion will return to the current situation in the future, as the population increases. True, but that doesn't make the investment pointless – quite the contrary.
The figure below shows what happens if the population increases from 10 to 15. This extends the horizontal scale, moving the starting point of the blue line to the right. As before, road investment moves the red line downwards. We thus move from point A to point D, where the displaced blue line crosses the new red line. Commuters once again take the car more than the train, and at the new equilibrium D the cost of congestion is exactly the same as at the initial point A (the figure is calibrated such that this is the case). Therefore, congestion remains unchanged. But the investment is useful, because without it road congestion would still be the dotted red line and the equilibrium would be at point E, with a much higher cost. In other words, population growth creates congestion, and investment reduces it.
This analysis is admittedly simple (the author is not, after all, an economist specialising in transport), but it highlights which comparisons are appropriate and which are not. As long as investment reduces road congestion (including at motorway exits) for a given number of cars, it reduces congestion. After all, if we believe that increasing capacity is a bad idea, then that implies that reducing it is a good one. But nobody is proposing that.