Speed and Space Management
What this domain tests
Speed and Space Management tests following distance, stopping distance, speed selection, and space cushions. The exam wants you to calculate a safe gap for a long vehicle and adjust it for load, weather, and traffic.
Core rules
- Use the length-based following rule: one second for each 10 feet of vehicle length at speeds under 40 mph; add one second at speeds over 40 mph.
- Total stopping distance includes perception, reaction, brake lag, and actual braking distance; a heavier load and wet pavement increase it.
- Keep a space cushion ahead, beside, and behind; avoid riding in another driver’s blind spot.
- Reduce speed before curves, off-ramps, work zones, and wet or icy pavement.
- Do not tailgate to prevent cars from cutting in; a larger gap gives you time and an escape route.
Worked example
A 60-foot combination traveling at 50 mph needs 6 seconds for length plus 1 second for speed over 40 mph, for a 7-second following distance. At 50 mph, 7 seconds is roughly 515 feet. The reasoning: the rule converts vehicle length into time, then adds a speed allowance so the gap grows as stopping distance grows.
Traps
Using the 2-second car rule for a 70-foot combination; maintaining the same gap downhill; and closing the gap in rain because traffic is slow.