A driver must reduce their speed to __________ mph when approaching a railroad crossing with explosive substances if traveling above that speed.

The correct answer is 20 mph. When approaching a railroad crossing that has the potential for explosive substances, there is a specific legal requirement to reduce speed to a maximum of 20 mph. This regulation is in place to ensure the safety of both the driver and any potential hazards at the crossing. Reducing speed allows for better control of the vehicle and ensures the driver has enough time to react appropriately to any unforeseen circumstances, such as a train approaching or other safety signals activated at the crossing.

Understanding this regulation is crucial for drivers since railroad crossings can pose significant risks, especially when explosives or hazardous materials are involved. Being aware of the required speed limit in such scenarios helps to reinforce safe driving practices and promotes public safety.