Curious Cows

American cattle ranchers in the Southwest invented the cattle guard (or grid) to prevent cattle from migrating across fenced boundaries. A great time saving invention, they allowed somewhat lazy ranch hands in their trucks to carry on without having to stop to open and close gates.

However, the grates were expensive and particularly uncomfortable for passengers and cargo to cross. So one day some bright cowboys, working on the assumption that cattle aren't as bright, experimented by painting lines across the road to simulate a cattle guard.