Trains don't run on regular streets. They need steel tracks to move. These train lines might encounter cars and concrete on their path, though. In such intersections a level crossing is needed. In modern times level crossings are always less and less. Several of them have been removed from our cities, but some others are still in service. To our eyes they all look beautiful and old fashioned in their authority to stop traffic. Red light, bars down: cars must stop. Green light, bars up: people can cross.