What Is the Stopping Distance of a Semi-Truck?

truck speeding down highway

The massive size and weight of semi-trucks make even basic driving maneuvers like stopping far more difficult and potentially dangerous. Understanding how much room a commercial vehicle needs to come to a stop could help keep you safe while driving in Alabama.

Below, we’ll discuss how truck brake systems work and how much space you should leave between your vehicle and a big rig.

Stopping Distance Statistics for Semi-Trucks

According to truck safety regulators, the typical stopping distance for a passenger car traveling at 65 mph is a little more than 300 feet. But a semi-truck with a full trailer (the maximum allowed weight for most trucks is 80,000 pounds) traveling at 65 mph needs more than 500 feet to come to a full stop.

That difference of roughly 200 feet can cause harrowing and potentially deadly collisions.

Brake System on Large Trucks

Most commercial semi-trucks use air brakes to slow down and stop. When a truck driver presses down on the brake pedal, a lever is activated that pushes a piston into the brake system’s master cylinder. The master cylinder fills with compressed air, and when the piston is activated, the cylinder pushes this compressed air through the truck’s brake lines. The compressed air puts pressure on the truck’s brakes and brings it to a stop.

Most car brake systems work similarly, except they use hydraulic fluid instead of compressed air.

While all the components of a truck’s braking system need to be kept in good condition, these parts are not the only things that can impact a truck’s stopping distance.

Safety regulators use the following factors to measure a truck’s total stopping distance:

  • Perception distance — How far a truck travels before the driver realizes they need to apply the brakes
  • Reaction time — How far the truck travels between the time the driver realizes they need to slow down and when they activate the brakes
  • Brake lag — How far the truck travels before the brakes start working after the driver activates them
  • Braking distance — How far the truck travels once the brakes have been fully engaged

By adding up all these factors, regulators can judge how far a truck will travel once the brakes are activated.

Factors That May Affect Stopping Distance

Many factors influence how much of a buffer a truck needs to stop. These external factors can include:

  • The weather
  • The road surface
  • The weight of the truck’s trailer and cargo
  • The condition of the truck’s brakes and tires
  • The truck’s speed before braking

Determining a Safe Following Distance for Large Trucks

As a general rule, truck drivers should leave about 1 second of the following distance for every 10 feet of vehicle length under 40 mph. Drivers should add a second at speeds over 40 mph. For example, a 60-foot truck traveling 60 mph should leave 7 seconds of the following distance.

If you are driving a truck in bad weather, you should double your following distance because trucks take longer to stop when the roads are slick.

Contact Our Experienced Truck Accident Lawyers for a Free Claim Review

If you have been injured in an Alabama truck accident, turn to a legal team with a proven track record of success. For decades, the experienced attorneys at Morris, King & Hodge have helped people injured by the negligence of truck drivers and trucking companies seek justice and fair compensation.

If you’ve been injured in a rear-end collision caused by a truck driver who failed to stop in time, contact us for a free consultation.

Harvey B. Morris is a lifelong Alabamian who has been practicing law in Huntsville since getting his law degree and passing the state bar in 1966.