Under what condition are drivers required to stop at a railroad crossing?

Drivers are required to stop at a railroad crossing when there is a flashing red light. This is a critical safety measure designed to prevent accidents between vehicles and trains. Flashing red lights serve as a clear warning that a train is approaching, indicating that it is unsafe to cross the tracks. Stopping ensures that drivers have the opportunity to look for trains before proceeding.

In contrast, simply hearing a whistle does not provide a guaranteed indication that a train is near; it may not be audible or may be too far away. Likewise, while the presence of downed barriers is a strong indicator that a train is coming, there are situations where the lights can flash even if barriers are not in place, so relying solely on barriers can be misleading. Finally, the notion that it's not necessary to stop contradicts established safety protocols at railroad crossings, where stopping is essential to ensure the safety of both drivers and train passengers.