When should drivers be most cautious while approaching railroad grade crossings?

Drivers should be most cautious while approaching railroad grade crossings when the lights are flashing because this indicates an incoming train. The flashing lights serve as a crucial warning system to alert drivers that it is unsafe to cross the tracks at that moment, as a train may be approaching at high speed. Recognizing and responding appropriately to these signals is essential for ensuring safety.

While it is certainly important for drivers to be cautious at all times near railroad crossings, the flashing lights specifically denote an immediate danger that requires urgent attention and action. Other conditions, such as low visibility or traffic volume, can also warrant caution, but they do not universally signal the presence of a train like the flashing lights do. Thus, the presence of flashing lights is a direct indication that drivers must stop and wait until it is safe to proceed.