There are 2 policemen parked along a one-way street looking for traffic violations. They spot a taxi driver going in the wrong direction, yet they do nothing. Why?
I'll be disappointed if the solution is that the taxi driver was on foot. If he was walking, what was the 'wrong direction'?
Perhaps the taxi driver took a wrong turn, so was going in "the wrong
direction" but not committing a traffic violation. The question
remains, of course, how the policemen would know this.