Unspreadable Jam

You can’t fix a traffic problem by improving the roads.

Let’s say that Main Street is very crowded. It’s a single-lane road and a thousand people per hour drive on it, making it a congested mess. People complain about it all the time the general consensus is that “something should be done.” So at great taxpayer expense, the city spends a ton of time and effort widening Main Street to two lanes. Now a thousand people per hour won’t congest it at all, and it would take twice as many people to bring it back to the level of traffic it had before.

That is what happens immediately.

Within the span of a few weeks to a few months, the road is every bit as congested as it ever was. The question is: why?

Well, we have to look at “what is unseen.” In the initial situation, a thousand people per hour drove on Main Street. But ten thousand people per hour made a conscious decision not to. Those other ten thousand people decided that they’d take an alternate route rather than face the traffic, or they’d choose an alternate destination entirely, or they’d stay home, etc. They might not take jobs at the other end of Main Street or eat at different restaurants or whatever else, because the traffic is so bad. The thousand people per hour who do drive on Main Street are those ones who have made the calculation that (even though they obviously don’t like the traffic) all their alternatives are worse.

But that calculation is ongoing, and the ten thousand potential drivers had different levels of commitment to the idea. For some people, the traffic was only just bad enough to make them choose an alternative (maybe the alternative is a road that also has traffic, but slightly less!). For others, the rest of the city would have to fall into the ocean before they’d ever drive on Main Street.

When the new construction is finished and the road is wider, the calculation changes.

Now Main Street has “openings,” let’s say. The next thousand people – the ones on the weakest end of the objection scale – now find that their objections are no longer sufficient to force them to choose alternatives. So they swap from whatever alternatives they had previously been choosing back to Main Street. And Main Street fills right back up.

And as the same amount of traffic congestion can now bring more people up Main Street, there’s further incentive for people to do things like open restaurants on the far end of Main Street and get jobs on that end and so on, so the incentive to go up that way intensifies – enough to counteract the negative response when the traffic starts to worsen again. An equilibrium is always reached, and the equilibrium will always be a lot of traffic.

There’s a lesson here, of course, well beyond just the lesson to civil engineers. The lesson is that whenever you see a problem that’s affecting a group of people, you need to understand that the group of people you see is only part of the overall situation. The problem itself is acting as a barrier to the people you don’t see – the potentials. That can work in your favor, if you want more people – if the congested checkout line at your store is preventing people from buying your stuff, then improving that line can make you more sales, even if the individual wait times don’t change.

But it can also be a danger. If you think that you can reduce the wait time at your free health clinic by adding more doctors, you can’t – because the reduced wait times will entice more people to show up until the wait times reach their previous equilibrium. There’s theoretically a number of doctors – or traffic lanes, or anything else – that can’t be overwhelmed in this way, but in practice that number is so high as to be impossible. You could reduce wait times to zero at your health clinic if there was one doctor for every citizen in your city, but that seems as unlikely as finally making that 40-lane-wide highway that no number of cars can clog.

The trick here is not to try to solve all problems of congestion. It’s to optimize the equilibrium. There is no perfect solution, but you can balance the needs of movement against everything else. Unfortunately, that often means not building more roads – which people tend not to like. But they only don’t like it because they believe (incorrectly) that traffic is a result of there not being enough roads. The reality is that as long as there is something people want, someone will be in line ahead of you to get it.

Optimize your patience, choose your own best alternatives, and live your best life.