Russell's Blog

Los Angeles traffic provides fertile grounds for situations that can be modeled with the Prisoner's Dilemma. It's not difficult to guess what strategy the owners of the Toyota Land Cruiser and the Chevy Tahoe have decided to play :

I encountered these two defectors in an extremely crowded parking structure in Old Town Pasadena. This isn't just antisocial behavior. The owners of these two titanic vehicles are also breaking the clearly written rules.

It occurs to me that the decision to buy these vehicles in the first place can also be modeled using many, many iterations of the Prisoner's Dilemma played against every other driver. Here's how such a model might be constructed. The options are :

• Buy an SUV (defect)
• Buy a compact car (cooperate)

In a single round of Prisoner's Dilemma, it is usually reasoned that the only rational choice is to defect. However, when two individuals play many iterations against one another, more interesting strategies can succeed. The strategy that seems to do the best in most situations is some variant of generous, randomly forgiving tit-for-tat. To apply the Prisoner's Dilemma to the automobile market, you must view the game as continuously ongoing because a player can trade in their car for a different model at any time, and the game is played against every other driver on the road. Each iteration makes a marginal contribution to the total outcome for the player. For example, the actual risk of death is the sum over the marginal risk of death arising from the outcome of each game.

The outcomes are :

		Player's Choice
		defect	cooperate
Stranger's Choice	defect	Punishment for Mutual Defection Both players buy an SUV, negating the advantages of owning a larger vehicle. Both players are penalized with substantial marginal increases in traffic congestion, gas prices, risk of death, risk of injury, and rate of damage to shared environmental resources.	Sucker's Payoff Player suffers moderate marginal increase of gas prices, traffic congestion, and rate of destruction of shared environmental resources than the Punishment for Mutual Defection. However, the player suffers a worse view of the road and substantially increased marginal risk of death and injury.
	cooperate	Temptation Player suffers a moderate marginal increase of gas prices, traffic congestion, and rate of destruction of shared environmental resources than the Punishment for Mutual Defection. They also enjoy better view of the road and a substantially reduced marginal risk of death or injury.	Reward for Mutual Cooperation Both the Player and the Stranger enjoy a better view of the road and substantial marginal reductions in gas prices, traffic congestion, rate of destruction of shared environmental resources, and risk of death and injury.

In computer models of the iterated Prisoner's Dilemma, and in real-world situations are well represented by the model, strategies that are "nice," "generous" and "forgiving" tend to thrive. These terms have a technical meaning here. "Nice" simply describes a strategy that will not defect first, "generous" describes strategies that will not retaliate against other players when they defect under some circumstances, and "forgiving" describes strategies that will "forget" about past defections of other players. Richard Dawkins describes this in some detail in The Selfish Gene (see Chapter 12: Nice Guys Finish First), basing much of his argument on the research of Robert Axelrod.

If the automobile market really can be modeled using the iterated Prisoners Dilemma, then we would expect to see the most successful strategies in Axelrod's tournaments, which are mostly "nice," become the dominant strategy for car-buying. That is to say, we should see mostly compact cars. So, why do people keep buying SUVs? They are playing Defect against the rest of us, hoping to receive the Temptation outcome from most of the iterations of the game.

This is especially curious because because both the Punishment for Mutual Defection and the Sucker's Payoff are very severe. It doesn't take very many people playing Defect to block the view on the road, to drive up gas prices, to dramatically increase the risk of death an injury for all drivers, and to accelerate the rate of destruction of our shared environment. The Reward for Mutual Cooperation should be a very strong attractor in the problem space.

It's very tempting to think of SUV buyers as stupid, or as assholes, or as sociopaths. However, it is more useful to model the decision as a purely rational decision based on what they think will be the best strategy. For most people, it probably isn't a rational choice, but that doesn't actually matter. In the model, we pretend that the players are playing as if they are making rational choices. This is how computers play Prisoner's Dilemma, even though they aren't capable of rational choices.

Game theory offers a fairly convincing (and rather grim) explanation for the phenomenon of SUVs. It makes less sense to play Cooperate if you don't think the game will go on for much longer. On the last round of the game, it becomes the classic, non-iterated Prisoner's Dilemma for which the only rational choice is Defect. Everyone knows that we're running out of oil. Consciously or unconsciously, people are behaving in a way that suggests that the shadow of the future is shortening.