Truck Stopping Distance

Semi-truck accidents lead to devastating consequences, including severe injuries, massive property damage, and–in many cases–loss of life.

Trucks are inherently dangerous because of their size and weight. A semi-truck needs more time to come to a complete stop than a regular passenger vehicle, meaning a truck driver would need to start braking sooner. So, how long does a truck take to stop? And what factors affect the stopping distance?

Stopping Distance: Difference Between Semi-Trucks and Passenger Vehicles

Fully-loaded semi-trucks weigh around 80,000 pounds, an enormous difference from an average weight of approximately 2,000 to 4,000 pounds for a normal passenger vehicle.

Large commercial trucks have more momentum than smaller vehicles while moving, meaning they need more time and distance to come to a complete stop. Hence, truck drivers are trained to estimate stopping distances accurately in various situations to avoid accidents.

The Federal Motor Carrier Safety Administration (FMCSA) estimates the typical passenger vehicle vs. semi truck stopping distance below:

A normal passenger vehicle traveling 65 miles per hour would require around 316 feet (about the length of one football field) to come to a complete stop;
A fully loaded semi-truck traveling at 65 miles per hour would require about 600 feet to stop (the length of around two football fields).

What Factors Affect Stopping Distance?

The stopping distances above are estimates under ideal conditions. The stopping distance of a large commercial vehicle may vary, depending on several factors, such as:

Weight: The mass and velocity of an object are directly proportional to its momentum, meaning if either mass or velocity increases, the object’s momentum increases in equal proportion. However, a large truck with a heavy load does not always require a greater stopping distance than a lighter or empty truck traveling at the same speed.

The reason is that the more weight a truck carries, the more heat the brakes absorb. Trucks that carry heavy loads usually have better braking systems to shorten the braking distance while taking massive amounts of weight.

Speed: A semi-truck traveling faster has greater velocity and momentum than a slower-moving rig of the same mass. The quicker a truck travels, the more time it needs to come to a complete stop.
Perception: Another factor that affects a truck’s total stopping distance is perception distance, which is the distance a truck travels before the driver recognizes the need to slow down or stop.
Driver’s Reaction Time: The faster a truck driver acts upon the need to stop or slow down, the shorter the truck’s stopping distance. It usually takes less than two seconds for drivers to recognize a dangerous situation and step on the brakes.

Truck drivers often have a faster reaction time since they can see obstacles from farther away because of the truck’s height.

Braking Distance: This element refers to the distance the truck travels from when the driver presses the brake pedal until the vehicle stops completely.
Brake Lag: Semi-trucks have different brake systems than regular passenger cars. Most passenger vehicles have hydraulic brakes, which use brake fluid and function faster than truck brake systems.

On the other hand, tractor-trailers have air brakes with lag time. Air brakes must build pressure along the brake lines before slowing down the vehicle.

Road Conditions: Rain, sleet, ice, snow, and other inclement weather conditions increase the stopping distance of semi-trucks and smaller passenger vehicles.

What Are the Stopping Distance Requirements For Semi-Trucks?

The National Highway Traffic Safety Administration (NHTSA) regulates interstate trucking and sets stopping distance requirements for tractor-trailers and other large rigs. According to the Federal Motor Vehicle Safety Standards (FMVSS) No. 121, the requirements for semi-trucks are:

Under the Loaded-to-GVWR: An air-braked single-unit truck weighing less than the Gross Vehicle Weight Rating (the maximum amount of weight a fully loaded commercial truck can bear) must stop within 310 feet when braking from 60 mph; an air-braked truck tractor must brake within 355 feet.
Underloaded: The truck must stop within 335 feet when braking from 60 mph.
In an Emergency: When traveling at 60 mph, a single-unit semi-truck driver must stop within 613 feet; a tractor driver must brake within 720 feet.

What is a Safe Following Distance When Driving Behind a Semi-Truck?

The average car stopping distance is 316 feet under ideal conditions. However, you should consider the FMSCA recommendations when driving behind a semi-truck. According to the agency, you should leave at least one second per 10 feet of vehicle length while traveling below 40 mph. Add another second when driving above 40 mph.

How to Avoid a Truck Crash: Tips For Car and Truck Drivers

Given the increased stopping distance of semi-trucks and other dangerous conditions associated with these large vehicles, alertness is crucial whenever you share the road with one. Remember the following tips to avoid a truck crash:

Stay out of a truck’s blind spots. Avoid driving near a truck’s blind spots as much as possible. Never drive too closely or attempt to pass it abruptly. Many devastating accidents occur when truck drivers fail to notice smaller passenger vehicles behind, beside, or in front of them.
Increase following distance: Slow down and increase your following space when driving behind a big rig, especially at highway speeds.
Never brake abruptly. The stopping distance of a semi-truck is much longer than a regular car because of the truck’s weight and air brake system. Thus, suddenly braking in front of a truck gives the driver insufficient time to stop and avoid a truck accident.

If You’re a Truck Driver:

Truck driving is an inherently risky job. Plus, there is an immense responsibility to keep other road users safe. Whether you’re driving an empty rig or a fully loaded truck, keep these safety precautions in mind:

Always follow stopping distances. Start braking within the recommended stopping distances as soon as you recognize the need to slow down or stop.
Never speed. The faster a vehicle travels, the longer it takes to stop and the higher the risk of a truck accident, especially if you’re driving a full tractor-trailer. Stay within the posted speed limits.
Be wary of other vehicles. Check your blind spots before turning, increase your following distance, and give enough warning to other drivers when merging. Alertness and awareness are the best ways to avoid a devastating truck accident.

Conclusion

Semi-trucks require greater stopping and following distances due to size, weight, and braking systems. Hence, agencies regulating the trucking industry sets stopping distance requirements for large trucks to minimize accident risks.

People in truck driving jobs have a huge responsibility for road safety when driving semi trucks. While trucking companies are responsible for training their employees, other drivers should also be aware of how a semi-truck operates on the road so they can keep themselves safe.