I was walking along the pavement, and someone was wheeling a bicycle in the opposite direction. I stepped onto the road so that we could pass, and he thanked me.
I wondered if he had applied Kant's test that if everybody rode bikes to work, would things work out okay? If so, I think he would have passed Kant's test, because there would be no cars on the road, and cycling would be fine and wouldn't interfere with pedestrians. However, a motorist applying Kant's test would also say that if everyone that rode a bike drove a car instead, then pedestrians would be able to walk along the pavement because cars (should) never go on the pavement.
I thought that there must be a better way to illustrate this flaw in Kant's thinking. Forget about bikes, how about this:
I'm driving on the left hand side of the road. If everyone drove on the left hand side of the road, all would be well, so according to Kant I'll carry on. Someone else is driving along on the right hand side of the road, and she reasons that if everyone else drove on the right hand side of the rode, all would be well. We crash, and thus refute that the Kantian approach works in all cases.