Stopping Distance / Following Time
Perhaps the best known defensive driving technique is to "Slow Down and Increase Following Distance." A non-professional driver might think this is just hyperbole if they have not been taught, or have forgotten the correct method of calculating "following distance."
"Following Distance" might more appropriately be termed "Following Time" because it is a function of time, as well as the size of the vehicle and the driving conditions.
To calculate Following Time:
- First, divide the length of the vehicle by 10.
- For example, a 65’ vehicle divided by 10 = 6.5.
- Therefore, the mininum following time should be 6.5 seconds.
- Safer Drivers add an additional second for speeds over 40 mph.
- Therefore, the minimum following time for a 65’ vehicle at 55 mph is 7.5 seconds.
To measure Stopping Distance;
- Select a stationary obect 12 to 15 seconds ahead such as an overpass, road sign, tree, or shadow.
- When the vehicle up ahead passes that object, begin counting in seconds ("One thousand and one, one thousand and two, one thousand and three, one thousand and four, one thousand and five, one thousand and six" etc.)
- If your vehicle gets to the same object just as 5 seconds elapse, then you might be following too closely. Slow down and, pick another fixed object and try again until your count reaches between 5 to 7 seconds, depending upon your vehicle length and driving conditions.
It is important to know that...
- At 55 mph, a motor vehicle is moving at 88 feet per second.
- The brakes, tires, springs, and shock absorbers on heavy vehicles are designed to work best when the vehicle is fully loaded. Empty trucks require greater stopping distances because an empty vehicle has less traction.
- Safer drivers are cognizant that when the road is slippery, they need much more space to stop so they reduce their speed and increase their following distance and seek the nearest safe haven to pull over and park it.