How long does it typically take for a tractor-trailer unit to clear a double track?

The correct answer, often approximated at 15 seconds for a tractor-trailer unit to clear a double track, reflects the time it generally takes for longer vehicles to safely navigate over railway crossings. This duration accounts for the length of the vehicle, the distance it travels, and the need for caution when crossing tracks, especially in areas where train traffic might occur.

A tractor-trailer unit is significantly longer than smaller vehicles, requiring additional time to completely clear the tracks. This is essential for ensuring safety, as trains can approach quickly and may not be able to stop in time if a truck obstructs the tracks. The 15 seconds approximation provides a buffer to ensure the vehicle is well clear of danger.

The other options suggest shorter or longer times. Shorter times would not accommodate the size of larger vehicles effectively, while longer times might not align with standard operational expectations for clearing tracks safely and efficiently. Hence, 15 seconds is a practical and realistic timeframe in the context of trucking safety and operations at rail crossings.