Speed and Space Management
What this domain tests
This domain tests whether you can choose a safe speed and keep enough space around a heavy vehicle. It includes following distance, stopping distance, and adjustment for weather, load, and traffic.
Core rules
- The basic speed law applies: never drive faster than is safe for conditions, even if the posted limit is higher.
- Following distance: use one second for each 10 feet of vehicle length at speeds below 40 mph. At higher speeds, add one extra second.
- Total stopping distance includes perception distance, reaction distance, and braking distance. Heavier loads and wet roads increase braking distance.
- Maintain side and overhead clearance, and avoid being boxed in. Leave room ahead for an escape path.
Worked example
A 70-foot combination travels at 55 mph. Base following time is 7 seconds; above 40 mph, add 1 second, for 8 seconds. At 55 mph, the vehicle covers about 81 feet per second, so the gap should be about 650 feet. A four-second car gap is far too small.
Traps
Using passenger-car following distances, ignoring load weight, and treating the posted limit as a target in rain or fog are common misses. Space management includes the sides and rear, not just the front.