Stopping Distance

Total stopping distance is the distance your vehicle travels from the time you slow down or brake until it stops. Total stopping distance is made up of several components:

  •  perception distance
  •  reaction distance
  •  braking distance

Perception distance is the distance a vehicle travels while a driver is identifying, predicting and deciding to slow for a hazard. Perception distance can be affected by visibility and the placement and motion of the hazard itself. Reaction time is the time it takes for a driver to execute a decision once danger is recognized. The distance your vehicle travels while you react is called a reaction distance.


Most drivers have an average reaction time of 3/4 of a second. A variety of factors can influence a driver’s reaction time, such as fatigue, drugs, alcohol, age and experience of driver.


Braking distance is the distance a vehicle travels from the time a driver begins pressing on the brake pedal until the vehicle comes to a stop. There are many factors that affect the braking distance of a vehicle, including:


Speed––higher speeds will cause the vehicle to take longer to stop.

Vehicle condition––tires, brakes and suspension all can affect braking distance depending on their condition.

Roadway surface—rain, snow, leaves, gravel and dirt can add to a vehicle’s braking distance.

Hills—braking distances will increase on a downhill grade.


With large tractor-trailers, there are a few other factors to be considered in stopping distance, including: 


Brake Lag Distance

The typical tractor-trailer is over 70 feet long. When a professional truck driver presses on the brake pedal, it takes time for that brake signal to travel to all the wheels on the tractor-trailer. All the time this signal is traveling to all the wheels, the truck is still traveling down the highway. The actual time is about 3/4 of a second. This delay is called “brake lag,” and the distance the vehicle travels in this amount of time is called “brake lag distance.”


Weight of the Vehicle

Tractor-trailers have much longer braking distances than passenger vehicles because of their heavier weight. Tractor-trailers and other large trucks are designed to haul many different loads of varying weights. As mentioned before, a typical tractor-trailer or other large truck can weigh as much as 80,000 pounds by law. Consequently, they have massive braking systems designed to allow them to safely stop. The heavier a vehicle is, the more energy it needs to stop. A lighter passenger vehicle will need less energy to stop than a large tractor-trailer.