Speed and Space Management
This domain tests speed selection, following distance, stopping distance, and traffic gaps. The exam wants numbers and adjustments for load, weather, and grade-not just 'drive carefully.'
Speed
Obey posted limits and adjust for conditions. Minnesota's default limit is 55 mph on rural two-lane roads, with 65 or 70 mph on many freeways. Slow down for curves, work zones, rain, snow, and heavy loads.
Following distance
Use one second per 10 feet of vehicle length at speeds below 40 mph, and add one second above 40 mph. A 60-foot vehicle needs 6 seconds below 40 and 7 seconds above. A 70-foot combination needs 7 and 8 seconds.
Stopping distance and gaps
Total stopping distance is perception distance plus reaction distance plus brake lag plus braking distance. At 55 mph, a loaded tractor-trailer needs about 400 feet to stop. To enter or cross traffic at 55 mph, you need a gap of about one-quarter mile.
Downgrades
Select a lower gear before the descent and use the engine brake; do not ride the service brakes, which can fade.
Worked example
A 70-foot combination travels at 55 mph. Reasoning: above 40 mph, the rule is 7 seconds plus 1 second for the extra 10 feet, so 8 seconds. If a car cuts in and leaves only 3 seconds, ease off and re-establish the gap rather than tailgate.
Traps that cost marks
Using car following distances; forgetting to add time for rain or ice; coasting in neutral downhill; assuming a light load stops shorter than a heavy one.