I used to drive (walk? ride?) every day by an old abandoned place on Kentucky Ave that's since been torn down. There was a sign on the gate at the entrance that said "Not enough room to clear man on side of car". I assumed it was meant for people who are driving a vehicle that might have a person standing on the outside, much like a garbage truck. It always did make me wonder though
A sign saying this, usually refers to a Rail Road Car, and warns that there is not enough room for a man riding on the car by standing on the bottom rung of the side ladder, to clear some sort of fixed object. You would usually see these on both sides of a gate where a rail goes through, or on the side of a building that a set of tracks run really close to.