A key factor in rear-end crashes is improper following distance. In order to determine how much following distance is required to bring a tractor-trailer to a complete stop, drivers first need to know how much stopping distance their vehicle requires. A tractor-trailer driving 65 mph travels at a rate of approximately 100 feet per second. A fully loaded tractor-trailer requires a minimum of 665 feet to reach a complete stop. The table below demonstrates how stopping distance is calculated.
Calculate Stopping Distance
| Seconds | Rate | TOTAL FTS | |||
| Perception Time | 1.5 | x | 100 | = | 150 |
| Reaction Time | 1.0 | x | 100 | = | 100 |
| Brake Lag | 0.75 | x | 100 | = | 75 |
| Braking Distance | 3.4 | x | 100 | = | 340 |
| TOTAL STOPPING DISTANCE = 665 ft. | |||||
Perception Time
This is the amount of time it takes a driver to perceive the need to stop, such as noticing the brake lights on the vehicle ahead. It takes a fully alert driver’s brain approximately 1.5 seconds to perceive the need to stop. At 65 mph, a driver will travel 150 feet before the brain perceives the need to react.
Reaction Time
This refers to how long it takes a driver to react and move their foot on the brake pedal. This takes approximately one second to perform. In this time, the vehicle travels an additional 100 feet per second.
Brake Lag
This is the time it takes for the air brake system to function. This is generally three quarters of a second. The truck will travel an additional 75 feet per second.
Braking Distance
This refers to how long it takes the truck to actually stop once the brakes are applied. Assuming the brakes are functioning properly and the tires have adequate tread and traction, a fully-loaded tractor-trailer could take an additional 340 feet to stop.
Total Stopping Distance
Add together the perception time, reaction time, brake lag, and braking distance to calculate the total stopping distance required by a tractor-trailer traveling at 65 mph. The sum is 665 feet.
At 65 mph, a fully-loaded tractor-trailer requires a minimum of 665 feet of stopping distance. The most reliable method drivers use to gauge this distance is by counting seconds. To do this, pick a stationary object on the side of the road, like a road sign or overpass, and, as soon as the vehicle in front passes your chosen object, begin counting: “one-one-thousand, two-one-thousand…”. Continue counting until your vehicle reaches that stationary object.
In general, establishing a minimum following distance of six seconds is necessary.
At 65 mph, keeping one second of following distance means the vehicle is traveling 100 feet behind the vehicle in front. It takes an automobile a minimum of 150 feet to stop. With a 100 foot gap plus the auto’s stopping distance of 150 feet, an impact would occur within 250 feet. Since it takes a truck 665 feet to stop, it is clear that one second of following distance will result in a rear-end crash. It is not until six seconds of following distance is established that a tractor-trailer has sufficient stopping distance. These are in ideal conditions. Add one additional second for each hazard present, such as rain.
We are here to answer your questions. Contact our Risk Management Specialist today!
Risk Management Specialist | Joe Morten & Son, Inc.
O: 865.392.3777 | C: 865.771.9506
This material is intended to be a broad overview of the subject matter and is provided for informational purposes only. Joe Morten & Son, Inc. does not provide legal advice to its insureds or other parties, nor does it advise insureds or other parties on employment-related issues, therefore the subject matter is not intended to serve as legal or employment advice for any issue(s) that may arise in the operations of its insureds or other parties. Legal advice should always be sought from legal counsel. Joe Morten & Son, Inc. shall have neither liability nor responsibility to any person or entity with respect to any loss, action, or inaction alleged to be caused directly or indirectly as a result of the information contained herein. Reprinted with permission from Great West Casualty Company.