CDL Driving Safely: Control Your Speed

Perception Distance

  • The distance your vehicle travels, in ideal conditions; from the time your eyes see a hazard until your brain recognizes it.
  • Average perception time is 1 ¾ seconds

Reaction Distance

  • The distance you will continue to travel, in ideal conditions; before you physically hit the brakes, in response to a hazard seen ahead.
  • Average reaction time is ¾- 1 second.

Braking Distance

  • The distance your vehicle will travel, in ideal conditions; while you are braking.
  • At 55 mph on dry pavement, it can take 216 feet.

Total Stopping Distance

  • The total minimum distance your vehicle has traveled, in ideal conditions; with everything considered, including perception distance, reaction distance and braking distance, until you can bring your vehicle to a complete stop.
  • At 55 mph, your vehicle will travel 419 feet.
  • Perception Distance + Reaction Distance + Braking Distance = Total Stopping Distance
  • The faster you drive, the greater the impact of your vehicle to stopping.
  • The heavier your vehicle, the more work the brakes must do to stop it.
  • Account for the road surface and its impact on your speed:
  • Slippery surfaces take longer to stop and it will be hard to turn without skidding.
  • Wet roads can double stopping distance.
  • Reduce speed by about one-third on a wet road.
  • On snow, reduce speed by half.
  • On ice, reduce speed to a crawl.
  • Slippery surfaces:
    • Shaded areas may remain icy after other areas have melted.
    • Bridges can freeze before the road will freeze.
    • Melting ice can make it more slippery as the water lays on top of ice.
    • Black ice is a thin layer of ice that is clear enough to see the road beneath it.
    • Rain is most slippery just after it begins as it mixes with the oil on the road.
    • Hydroplaning occurs when a vehicle hits water or slush and the tires lose their contact with the road and have little to no traction.
      • You can regain control by release the accelerator and pushing in the clutch.
      • Do not use brakes to slow down.
      • Can occur as low as 30 mph
      • More likely if tire pressure is low or tread is worn
      • Can also happen on standing water


  • Adjust your speed for curves on the road.
  • If you take curves too fast:
    • You can lose traction and skid off the road.
    • You can keep traction and the vehicle can roll over.
  • Slow to a safe speed before you enter the curve.
  • Try not to brake, instead, start the curve slow and accelerate as you go through a curve.

Distance ahead

  • Be able to stop within the distance you can see.
  • Be aware of the impact of fog, rain and darkness.


  • Speed will increase on downgrades because of gravity.
  • Do not exceed “Maximum Safe Speed.”
  • Use the braking effect of the engine to control your speed.
  • Shift to low gear and save your brakes to slow down or stop.

Work Zones

  • Observe the posted speed limits.
  • Decrease even further when worker is close to a roadway.

Traffic Flow

  • In traffic maintain speed with other vehicles.
  • Use caution when changing lanes or passing.
  • Pay attention to traffic speed as well as posted road speeds.
  • Driving faster to save time will not be safer.