For a truck and trailer combination that is 20 m in length, what is the recommended following distance?

Answer: C — 7 seconds

The recommended following distance for a truck and trailer combination that is 20 meters in length is 7 seconds. This following distance is advised to ensure safety, especially given the size and weight of such vehicles. Trucks and trailers typically require more time to stop compared to smaller vehicles due to their mass and braking dynamics. A 7-second following distance allows the driver ample time to react to sudden changes in traffic conditions, providing a buffer that accommodates the longer stopping distance required for larger vehicles. This duration is based on a general rule of maintaining one second of space for every 10 feet (3 meters) of vehicle length, which is essential for safe driving in various weather and road conditions. In comparison, shorter following distances may not provide sufficient reaction time, especially in emergency situations. This is particularly relevant for large combinations like trucks and trailers, which can experience increased stopping distances when fully loaded or going downhill. Therefore, a 7-second gap is critical for maintaining safe operation on the road.