A Primer On Speed Management – Part I

As a safe, professional truck driver, you know that maintaining proper speed management at all times is absolutely necessary for the safe operation of your vehicle. Of course, this would include being mindful of the condition of the road, as well as traffic speed, flow and overall visibility.

In order to properly manage your vehicle’s speed, you have to understand the four factors that make up stopping your vehicle:

  • Perception distance;
  • Reaction distance;
  • Brake lag distance;
  • Braking distance, and;
  • Total stopping distance

Let’s take a closer look at each of these factors.

Perception Distance

Perception distance is marked by the distance a vehicle travels from the moment you see a hazard to the moment that visual realization is recognized in your brain. For an alert truck driver, perception time is generally three-fourths of a second. Keep in mind that at 55 mph, your vehicle travels approximately 60 feet in three-fourths of a second.

Reaction Distance

Your reaction distance is measured by the distance your vehicle travels from the moment your brain has recognized a hazard to the moment your foot hits the brake pedal. Your average truck driver has a reaction time of around three-fourths of a second. This means at 55 mph, you would have traveled an additional 60 feet, 120 total from the moment you recognized the hazard to the moment the brakes engaged.

Brake Lag Distance

For a normal commercial motor vehicle operating under normal conditions, brake lag distance generally comes in around a half-second. This is the amount of time it takes for the actual mechanical operation to complete.

Braking Distance

Braking distance is described by the distance it takes for the vehicle to come to a complete stop once the brakes have been applied. Braking distance can vary based on a number of factors, from the weight, length and speed of the vehicle to the current road conditions.

For heavy commercial motor vehicles, the braking components are designed to work best when the vehicle is fully loaded. At 55 mph under optimal conditions, a fully loaded commercial motor vehicle typically travels 170 feet and can take up to 5 seconds to come to a complete stop.

Total Stopping Distance

When combined, all of these factors equal your total stopping distance. When perception, reaction, brake lag, braking time and distance are added together at 55 mph under optimal conditions, it will take between 6 and 7 seconds for the vehicle to come to a complete stop. At higher speeds, stopping distance and time will increase.

Speed and Visibility

The most important thing to remember is that you must always be able to stop within your field of vision. Put more simply, you should be able to stop within the distance you can visually see ahead of you.

If you are driving at night or in poor weather conditions, weather it be rain, fog, sleet or wintry snow and ice, you must slow down to account for your field of vision. If you are outpacing the visual obstructions in front of you, you’re putting yourself and those around you at greater risk.

Speed and Traffic Flow

When you are operating in heavy traffic, the general rule of thumb is to follow the speed of the vehicles around you, provided you can maintain adequate following distances and aren’t traveling above the posted speed limit. If you find you are unable to keep at a safe distance, reduce your speed by 3 or 4 mph until optimum safe distance has been reached.

In many cases, drivers believe that exceeding the posted speed limit will save time, but when you’re operating in traffic, that isn’t always the case. If you travel much faster than those around you, you will find the need to be constantly passing other drivers. This increases your chance of being involved in an accident.

Driving faster than you should can also lead to fatigue and further increase your chances of being in an accident. So why risk it? It’s best to always go with the flow of traffic when it is safe and legal to do so.

Join us next week when we dive into Part II of our series and examine how road conditions can affect your speed management.