Stopping distance is the distance needed to bring a moving vehicle to a complete stop. Understanding this principle is incredibly important.
If you’re not able to accurately calculate stopping distance, you run the risk of a serious accident. That could result in property damage and bodily injury to yourself and others. It could even result in death.
The following driver safety facts give you the information you need to help you control and stop your vehicle.
Perception time is the three-quarters of a second it takes for you to realize you need to break - after your eyes see a hazard. So, if you’re driving at 65 mph, your vehicle will travel 71 feet before you realize you need to start braking.
Reaction time is also three-quarters of a second. By the time you move your foot from the accelerator to the brake, three-quarters of a second have passed. Again, at 65 mph, that’s another 71 feet traveled.
So far, your vehicle has traveled 142 feet and you haven’t even touched the brake.
Braking distance is the distance it takes to stop your vehicle once you apply the brakes. At 65 mph, it takes an additional 5.5 seconds or about 525 feet of actual brake application to stop your vehicle.
Stopping distance is the total distance needed to bring your vehicle to a complete stop. To determine the stopping distance, you calculate:
Perception Distance (71 feet) + Reaction Distance (71 feet) + Braking Distance (525 feet) = Stopping Distance (667 feet)
Common sense tells us that when conditions change, times and distances change with them. Among the factors that increase total stopping distance include:
- Age of equipment
- Speed
- Traffic
- Weather
- Road surface
- The weight of your load
It's important to know that an empty truck requires a greater stopping distance than a fully loaded truck, because an empty truck has less traction. That means there’s less friction between the tires and the road. An empty truck may also bounce and lock up its wheels, resulting in poor braking capacity.
Wet roads can significantly reduce your ability to stop your vehicle. In general, wet roads can double your stopping distance. In order to stop a vehicle on a wet road using the same stopping distance as a dry road, you’ll need to drive slower.
On wet roads, you should reduce your speed by about one-third. For example, slow down from65 mph to around 43 mph. On snow-covered roads, you should reduce your speed by at least one-half. This will help ensure that you have an adequate stopping distance.
Before traveling on potentially hazardous and slippery roads, be aware of these common dangers:
- Shady sections of the road stay wet and icy longer than sunny sections.
- Bridges freeze before road surfaces.
- When ice begins to melt, road surfaces become wet and slippery.
- Black ice makes a road appear wet, but in actuality, the road is frozen over.
- Icy vehicle mirrors and antennas are good indicators of impending icy roads.
- When it first begins to rain, water mixes with oil from vehicles, making roads extremely dangerous.
Driving too fast for conditions is defined as traveling at a speed that is greater than a reasonable standard for safe driving.13 Examples of conditions where drivers may find themselves driving too fast include: wet roadways (rain, snow, or ice), reduced visibility (fog), uneven roads, construction zones, curves, intersections, gravel roads, and heavy traffic.14 The Large Truck Crash Causation Study (LTCCS) reported that 23 percent of large-truck crashes occurred when commercial motor vehicle (CMV) drivers were traveling too fast for conditions.15
Below are some tips that will help you maintain a safe speed for various driving conditions.
TIP #1: Reduce Your Driving Speed in Adverse Road and/or Weather Conditions
Adjust your speed to safely match weather conditions, road conditions, visibility, and traffic. Excessive driving speed is a major cause of fatal crashes,16 and higher speeds may cause more severe crashes.17 The Fatality Analysis Reporting System (FARS) recently reported that 25 percent of speeding-related large-truck fatalities occurred during adverse weather conditions.18
Did You Know? You should reduce your speed by 1/3 on wet roads and by 1/2 or more on snow packed roads (i.e., if you would normally be traveling at a speed of 60 mph on dry pavement, then on a wet road you should reduce your speed to 40 mph, and on a snow-packed road you should reduce your speed to 30 mph). When you come upon slick, icy roads you should drive slowly and cautiously and pull off the road if you can no longer safely control the vehicle.16
Did You Know? When it first starts to rain, water mixes with oil on the road making it particularly slippery.16
Did You Know? Manufacturers generally advise drivers not to use a retarder [also called a "Jake" brake] on wet or slippery roadway conditions. In fact, a Safety Board Investigation of a motor coach crash that occurred in Canon City, Colorado, in December 1999, revealed that an enabled retarder most likely triggered the loss of control and eventual crash of the motor coach on a snow-covered and mountainous roadway.19
An example of a driver traveling too fast for conditions is shown in the video clip below. Training exercise questions follow the video clip.
VIDEO DESCRIPTION: The CMV driver is traveling on a multi-lane highway on wet pavement at night. Traffic is heavy and moving slowly. The driver is inattentive and traveling too fast for conditions. Traffic slows as the driver passes an emergency vehicle on the side of the road and the driver has to brake quickly to avoid hitting the lead vehicle.
TRAINING EXERCISE: After viewing the video, try to answer the following questions:
- Did the driver adjust his vehicle's speed considering the traffic, road, and weather conditions?
- What caused the driver to brake excessively?
- What could the driver have done differently?
TIP #2: Enter a Curve Slowly
Speed limits posted on curve warning signs are intended for passenger vehicles, not large trucks. Large trucks should reduce their speed even further. Studies have shown that large trucks entering a curve, even at the posted speed limit, have lost control and rolled over due to their high center of gravity.16
Did You Know? 40 percent of speeding-related fatalities occur on curves.20
Did You Know? Braking in a curve can cause the wheels to lock up and the vehicle to skid.16
An example of a driver traveling too fast for conditions is shown in the video clip below. Training exercise questions follow the video clip.
VIDEO DESCRIPTION: The CMV driver is traveling on an undivided two-lane road at night. The driver passes a curve warning sign but fails to reduce his speed. The driver is traveling too fast when he enters the curve and has trouble maintaining control of his truck. The driver has to brake hard and crosses onto the right shoulder.
TRAINING EXERCISE: After watching the video, try to answer the following questions:
- Did the driver slow down enough to safely enter the upcoming curve?
- What behavior indicates that the driver is driving too fast for conditions?
- What could the driver have done differently?
TIP #3: Reduce Your Speed Before Entering an Exit/Entrance Ramp
Approach an exit/entrance ramp at a safe speed. Truck rollovers are more likely to occur on exit/entrance ramps when the driver misjudges the sharpness of the ramp curve and enters the curve at an excessive speed.21
Did You Know? The posted speed limit on an exit/entrance ramp generally shows the safe speed for a passenger vehicle; the safe speed for a large truck is usually significantly lower than the posted speed.13
Did You Know? Even though ramps and interchanges make up less than 5 percent of all highway miles, 20 to 30 percent of all large-truck crashes occur on or near ramps.22
TIP #4: Drive Slowly with a Loaded Trailer
Be more cautious with a loaded trailer. Loaded trailers have a higher center of gravity and sudden speed adjustment may cause the load to shift, leading to skidding or a rollover.16
Did You Know? Large trucks with fully loaded trailers are 10 times more likely to roll over than those with empty trailers.23
Did You Know? Loaded trailers require 20 to 40 percent more braking distance than passenger vehicles to come to a complete stop.24
TIP #5: Slow Down in Work Zones
Before entering a work zone, decrease your speed, merge into the correct lane well ahead of any lane closures, and be prepared to slow down or stop suddenly.25 Speed increases perception-reaction distance, braking distance, and stopping distance.17
Did You Know? Nearly a quarter of all work-zone deaths in 2006 involved a large truck.26
Did You Know? In October 2003, a CMV driver was traveling at 60 mph in a 45 mph work zone on the Jane Addams Memorial Tollway in Illinois. The truck driver rear-ended a 25-passenger bus. The crash caused a five-vehicle pileup, killing 8 women and injuring about a dozen others. As a result of the crash, the truck driver was charged and convicted of reckless homicide and sentenced to 4 years in prison.27,28