Controlling Speed
Controlling Speed tests whether you choose a speed that matches the road, weather, visibility, and load-not just the posted limit. The exam stresses that speed too fast for conditions is a leading crash cause.
Speed and stopping distance
Stopping distance rises with the square of speed. If you double speed, you need about four times the distance to stop, plus reaction distance. Wet, icy, or gravel surfaces reduce traction and lengthen distance further. On curves, slow before the curve; braking in the curve can cause a skid or rollover.
Grades, work zones, and traffic
Downshift before a downgrade and use engine braking. In work zones, obey posted limits and watch for workers and narrow lanes. In traffic, keep a cushion and adjust speed early rather than tailgating.
Worked example
A 30 mph road becomes a 55 mph highway, but rain has just started. Reasoning: the limit is 55, but wet pavement and oil make 55 unsafe. Choose a lower speed, increase following distance, and brake earlier.
Traps
Treating the posted limit as a target in fog or rain, riding the brakes downhill, and entering a curve too fast cost marks. The correct speed lets you stop within the distance you can see and control the vehicle.