June 08, 2007
Highway merging and the theory of evolution
Some time ago, I wrote about the best way for traffic to merge on a highway, say when a lane is closed up ahead. There are those drivers who begin to merge as soon as the signs warning of impending closure appear, thus making their lanes clear. Others take advantage of this lane opening up to drive fast right up to the merge point and then try to squeeze into the other lane.
I said that although people who followed the latter strategy were looked upon disapprovingly as queue jumpers, it seemed to me like the most efficient thing to do to optimize traffic flow was to follow the lead of the seemingly anti-social people and stay in the closed lane until the last moment since that had the effect of minimizing the length of the restricted road. To merge earlier meant that one had effectively made the restricted portion longer.
Some commenters (Gregory Szorc, another Greg, and Jeremy Smith) disagreed with me, saying that what is important is not the length of the restricted road section but the ability of traffic to maintain speed. After all, a single lane of cars can travel quite smoothly at 60 mph for quite a distance, even if there is a lot of traffic. They said that the best thing to do is to merge into the other lane whenever you can do so without significantly losing speed. Clearly this means merging as soon as possible, when traffic is still light, rather than following my suggestion of waiting until the latest moment when traffic is heavier and merging has to be done at a low speed.
The last month I have been doing a lot of highway driving and have been observing this again and realize that I was wrong and the commenters right. When traffic is light, people can merge at any point and not back up traffic because the speed at which they merge is close to the normal speed. So it seems that the key feature is the ability to maintain speed and to merge when you can do so, which means when the traffic flow is light, which usually is well before the actual lane closing. In fact, I think that highway workers should post signs many, many miles ahead of the restriction and recommend that people merge as soon as possible.
But highway signs alone are not going to be enough to have the desired effect. What is needed is widespread public awareness of the benefits of merging well before you actually have to.
Of course, there will always be people who 'cheat' and try to go as far as possible along the closed lane and thus end up slowing traffic at the merge point and destroying the benefits for all. What can be done about this?
Interestingly, this phenomenon parallels the problem of explaining altruistic behavior using evolution by natural selection. It is easy to argue that a group benefits if all its members practice some particular trait, say by sharing food equally all the time so that everyone survives in both good times and bad. But the catch is that evolution by natural selection works on the basis of what is good for a single organism, not for groups, because it is an organism that has genes and propagates it. And that means that a cheater (i.e., someone who, when he has plenty, hides some of his food without being caught) benefits more than the others and is more likely to survive. If this tendency to cheat is an inherited trait, then over time cheaters will come to dominate in the population. Evolutionary biologists have developed theories on how to explain the evolution of altruistic behavior in the face of this seeming advantage for cheating.
In the case of highway merging, if everyone, without exception, follows the early highway merging rule, then long bottlenecks could be a thing of the past, unless traffic is so heavy that merging at normal speed is just impossible. But the occasional cheater will get a short-term benefit of getting a long stretch of open road, while the people behind him get the negative effects of having him slow down traffic at the merge point. So he gets the benefit of others merging early while others bear the cost of his cheating, making cheating an advantageous option to that single organism.
Of course, I am not suggesting that selfish and inconsiderate highway driving habits are inherited traits that will spread in the population by being passed down to the inconsiderate driver's children via his or her genes. But they could be like a 'meme', a mental virus that, like a gene, is a replicator that seeks to propagate and increase its incidence in the population, which in this case consists of the minds of people. This meme would encourage people to benefit themselves in the short-term at the expense of others, even though in the long term they too lose when someone else practicing the same behavior slows down traffic ahead of them.