Caditz/Newman

Our thoughts about autonomous vehicles and traffic flow

Game Theory and Rules Compliance

Why there are always cheaters

 

I am reminded of the cab driver who, block after block, ran full speed through red signal lights. When he did however stop at a green light, his passenger asked 'why did you run all the red lights and stop at this green light?'. The driver responded 'Why? There might be another cab driver coming on the cross road! '

Imagine a city where every driver fully complies with all traffic laws. In this city, driving would be extremely predictable. For example, we know that every driver would stop at every red light and every stop sign, even when there is no cross traffic. Let us now introduce a single law breaker, call him 'L.B.', into this city. L.B. would have an advantage because, given the predictability, he would incur very little risk in disobeying rules of the road and, by breaking rules will arrive at his destination sooner.

On the other hand, let's imagine a city where every driver behaved like our law breaker L.B. Accidents in this city would be commonplace. A careful driver, let's call her C.D., would now have an advantage because she would likely avoid collisions and arrive unscathed at her destination.

Game theory tells us that no pure state of all C.B.s or all L.B.s is stable. An equilibrium exists where the driving population consists of a certain balance of law complying and law breaking drivers. This is a particular instance of what is commonly called the 'Hawk Dove' game.