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

Answer: C — More than 15 seconds

A tractor-trailer unit typically takes more than 15 seconds to clear a double track due to its size and longer wheelbase, which affects its maneuverability. When crossing tracks, the vehicle's speed, length, and the layouts of the tracks all play significant roles in determining crossing time. In general, larger vehicles such as tractor-trailer units require more time to safely navigate across tracks while ensuring that the entire vehicle has cleared them before moving on. The additional time accounts for the possibility of slow acceleration and deceleration rates, particularly if the unit is loaded. Being aware that a tractor-trailer can take longer to clear tracks than smaller vehicles is crucial for safe driving practices and preventing accidents at rail crossings.