Monday, July 25, 2005

The Automobile: A Negative Sum Game

To understand why people drive so much, it is useful to compare transportation with a model negative-sum game.

In this model game, you have a choice of two moves. One possible move adds 100 points to your score but subtracts 1 point from the score of everyone near you. The other possible move adds 50 points to your score and does not change anyone else’s score.

Obviously, everyone will make the first move to get 100 points. If there are many people near each other, this choice will give everyone a lower score than if they all chose the second move. But if you act on conscience and choose the second move, it will not do any good: everyone else will still choose the first move, and you will hurt yourself by lowering your own score. The only way for the average person to get a higher score is for people to get together and agree that everyone will choose the second move.

This game is similar to the choice that people face when they decide on their mode of transportation. Choosing to drive is about twice as convenient as choosing alternatives on most trips: it will get you there faster and be more comfortable. But choosing to drive imposes a small cost on other people: it increases congestion, noise, parking problems, the risk of accidents, and so on for everyone who is near you. Alternatives, such as walking, bicycling, or taking public transportation, create social costs that are so much smaller than the automobile that they are negligible by comparison.

Obviously, everyone will choose to drive, even though they would be better off if all they chose alternatives. If you act on conscience and choose an alternative, other people will still choose to drive, and you will just be worse off than you would have been if you had chosen to drive.

Traffic congestion shows most clearly that this is a negative-sum game. On many freeways, traffic averages 25 miles per hour or less during rush hour. If everyone carpooled instead of driving alone, it might take an extra ten minutes for the average person to pick up carpoolers, but half the cars would disappear and traffic would be able to flow at 60 mph, so the overall trip would be much faster. But if a few people act on conscience and carpool, they have to take the extra ten minutes to pick up carpoolers but they still face the same congestion on the freeway, so their overall trip is longer.

With transportation, as with the model negative-sum game, the only way for the average person to be better off is for everyone to get together and agree that they will use alternatives to driving alone. This agreement must take the form of laws limiting driving.


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