When you are approaching a railroad crossing and a train is coming, you must stop _________ from the tracks.

Explanation

It takes much longer for a moving train to stop (up to a mile in most cases) than for a passenger car. If a train is coming, all vehicles must stop no more than 50 feet and no less than 15 feet from the tracks. Trains are at least six feet wider than the tracks, so you don't want to get too close to the tracks.