Game theory and the law

A picture:

and an explanation:

The local sheriff’s office had established the signs as a “ruse” to direct motorists to exit off the highway after viewing the warning of the upcoming DUI/Narcotics checkpoint. In fact, there was no checkpoint further down I-40. Instead, the sheriff set up a checkpoint at the end of the ramp of the first exit available to motorists after the posted signs, an exit not frequently used since no services were offered at the exit.

Separating equilibria do in some cases exist.