Safety & service
How Speed and Vehicle Weight Affect Stopping
Two delivery trucks can approach the same intersection at the same speed and respond differently when their drivers brake. Cargo, tires, road surface, brake condition, and grade all matter. The practical lesson is to leave a margin for the truck you are actually driving. Assuming that a loaded vehicle will stop like yesterday's empty one is a poor substitute for understanding its response.
Speed changes more than the arrival time
A moving vehicle carries kinetic energy, which increases with the square of its speed. For the same vehicle mass, doubling speed produces four times the kinetic energy. That is a physics relationship, not a promise that every real stop will follow an exact multiplier. The tires and braking system still determine how the vehicle converts that energy while slowing.1
Higher speed also means more ground covered before braking begins. During the same amount of recognition and response time, a vehicle traveling faster moves farther. A driver approaching a busy intersection too quickly therefore gives away space before the brakes have done any work. Slowing earlier addresses both the time available and the energy involved.
Weight creates demands without a simple multiplier
More vehicle mass means more energy to manage at the same speed. However, saying that twice the weight always means twice the stopping distance is inaccurate. Tire loading, available grip, brake design, load distribution, and operating condition interact. Commercial driver guidance also cautions that an empty heavy vehicle does not necessarily stop more effectively than a properly loaded one.2
For Sigma Continental drivers doing route work, the useful question is how the truck behaves within its rated limits. Know the vehicle and axle limits, follow the approved loading plan, and report changes in handling or braking. A route with many deliveries changes the load during the day, so yesterday's impression or the morning's feel should not become an assumption for every later stop.
Grip and heat set practical boundaries
Effective vehicle braking depends on usable tire grip at the road surface. Rain, ice, loose material, worn tires, and uneven surfaces can reduce that margin. Adding pedal pressure cannot create traction that is not available. Avoid treating electronic aids as permission to keep a dry-weather speed when the surface changes.
Long or steep descents add another demand: controlling heat. Commercial driver guidance warns that excessive brake heat can cause fading and reduced stopping effectiveness.3 Select the appropriate gear and speed before the descent, follow training for the specific vehicle, and avoid discovering halfway down that the truck is moving faster than its braking plan allows.
Turn the physics into an earlier decision
Before leaving the terminal, understand the day's vehicle and load. Once moving in a safe area, pay attention to normal braking response without conducting an improvised emergency-stop test. Approaching a downgrade, traffic queue, or changing weather, reduce speed and preserve more room while there is still time to do so gradually.
For a FedEx contractor, dependable service depends on drivers making these adjustments before a hazard develops. Choose a speed that fits the vehicle, load, and road, and reassess that choice whenever one of those conditions changes. A comfortable stopping margin comes from that whole assessment, not from a single advertised braking distance or a confident assumption about weight.
Sources and further reading
Review current guidance and follow the training and procedures provided for your role.
- Original Safety Articles collection
- OpenStax Rice University — Work Power and the Work Energy Theorem
- Georgia Department of Driver Services — Commercial Driver Manual Section 2 Point 6 Controlling Speed
- Georgia Department of Driver Services — Commercial Driver Manual Section 2 Point 16 Mountain Driving
