An earlier version of this article was published in 2015.
What to do to avoid congestion traffic in big cities? The question is a recurring one, and has been asked numerous times throughout automotive history. It is, in fact, the key issue of urban mobility based on the private vehicle. A priori, one of the most intuitive answers is “make more roads”. If congestion is the result of too many cars driving in a limited space, why not expand that space?
Contrary to what our logic might suggest, building more roads to reduce the horrible traffic in big cities would lead to even more traffic, not less. It is a very simple law that has been in place for decades, has been studied by mobility researchers frequently, and goes by various names: The Iron Law of Congestion, the Lewis-Mogridge Position, or the Triple Convergence. Whatever its name, its conclusion is the same: if you create more roads, you induce demand artificially.
You cause more traffic jams.
Despite the fact that the idea is old and has a long history within social research, the authorities do not usually take it very much into account. Up to now. A few years ago, the California Department of Transportation (California DOT) publicly recognized the futility to build more high-capacity roads to reduce traffic congestion. Contrary to the conclusions reached by their Connecticut counterparts, increasing the state’s transportation routes neither brings more economic benefits to the region nor does it solve the problem.
It’s a simple idea and put into practice every Thanksgiving, where cities like Los Angeles sink into endless traffic jams. It is explained in detail by Anthony Downs, a veteran economist, in numerous writings. This is one of them, very easy to read. When creating more roads, the logic says that part of the flow of vehicles stuck on one road will choose the new one. The same number of vehicles and more space, less traffic jams. But it is not that simple.
The behavior of the rest of the agents varies when you build a new belt, and you can do it in three different ways:
- On the one hand, drivers who they got up early more than they should to avoid rush hour traffic congestion will stop doing so. With more roads meeting the demand, they will have no incentive to continue getting up at five in the morning. Ergo: more cars are added to the existing tracks and those of recent construction.
- On the other, many drivers who used alternative routes and secondary schools to go to work will begin to use the new roads, highways and accesses offered by the administration, using the same principle that leads the early riser to stop being an early riser.
- And finally, an undetermined number of workers who previously opted for the bus, the train wave bike to go to their office they will stop doing it. The car is more comfortable and private, and, in theory, the new roads allow them to avoid the traffic jams that previously pushed them to look for alternatives. Now many will no longer feel the need to do so.
Everyone will occupy the old and new roads at the same time as everyone else. The congestion doesn’t go away, it just gets bigger and spreads to other roads.
How to fix a traffic jam
Outcome? Induced demand and more traffic, not less, circulating. Downs admits that in the short term the load of vehicles on the road is eased, but that in the long term more drivers will have more incentive to use their cars, and that the effect of expanding the network will have been neutralized. The DOT itself has reached the same conclusion, but with data: increasing the capacity of the tracks by 10% causes an increase of 3% -6% in the short term in the number of cars, and in the long term, 6% -10% .
It’s what Wes Marshall compares to “loosening your belt to cure your obesity.” A false solution to congestion. So if this doesn’t work, what alternatives do cities have? According to Downs, very few.
For him, traffic jams are the price to pay for order us economically the way we do it. Our economy depends on workers interacting with each other, and for this they have to do it at the same times. Logically, they will have to go to work at the same time. And if at the same time we want to live in areas of low population density (especially in the United States), the inevitable result is traffic jams.
Other alternatives are either politically unthinkable or economically too costly. For example, a good way to end traffic jams would be by introducing severe tolls on access roads to the city, a hot debate in Spain. Few politicians have the incentive to do so. More public transport? It’s an option, but research on the subject doesn’t always yield uplifting results. More roads? We have already seen that no, unless we turn our cities into gigantic masses of asphalt.
The last option is also inefficient for another reason. Our roads they cost a lot of money, much more than our taxes pay. In many ways, highways are as subsidized as public transport, even if we do not want to pay the price. In the United States and increasingly in Europe, it is a serious problem: the country’s infrastructure needs to be repaired, but there are no political incentives to maintain them. Adding more asphalt would only compound the problem.
Image: Marcel Sala / Flickr