Why do trains run with their headlights on? Answer: better visibility. Why do interstate buses (Greyhound, Trailways etc.) run with their headlights on? Better visibility. Why do all the countries in Europe, Scandinavia, Russia and Canada require either daytime running lights or mandate that drivers without daytime running lights turn on their headlights? Answer: better visibility to other drivers.Why doesn't the United States require daytime running lights, or require drivers to turn on their lights at all times? Answer: There is no good answer, period!