Safe Driving Distance

"I would like you all to give me a round of applause as I have not crashed my car in over 15 months"-Matthew Perry

When I was in High School and took Drivers Ed, the rule for safe driving distance was one car length for every 10 miles per hour. But that rule is not so easy to use in practice. Can you visualize the difference between five and six car lengths while driving?

Studies show that most people require a second and a half to respond to a stimulus. So if the guy in front of you hits his brakes, your eyes see it, the image goes to your brain, your brain thinks "I better do something", sends the command to your foot, and finally (a total of 1.5 seconds) your foot BEGINS to hit the brake pedal. If you're tailgating at high speed and only a car length behind - you may well crash into the leading vehicle before you ever have a chance to brake.

In New York State the recommended safe driving distance is 2 seconds for speeds under 40 mph. Above 40 mph the recommended distance is 4 seconds. The site SmartMotorist.com takes the average and recommends 3 seconds at all speeds. What does this mean? How do you follow 3 seconds behind?

Pick a landmark alongside the road like a lamppost, road sign, tree, etc. When the rear bumper of the car in front of you passes it, start counting - one hundred thousand, two hundred thousand, and so on until you reach the landmark with your front bumper. That is your driving distance. Now be sure to pad your counting with "hundred thousand" or "Mississippi" to get a full second with each number.

Is 2-4 or 3 seconds the final answer? No. These numbers only apply to perfect driving conditions. NY State recommends you add more time for

Twilight or Dark +2 seconds
Fog +1 second
Rain or Snow +1 second
Old Age +1 or 2 seconds
Sleepy or jetlagged +1 or more seconds
Distracted (cell phone, eating) +1 or more

These numbers are cummulative. So if you're driving on the interstate late at night in the rain and a bit tired then

2 + 2 (>40 mph) +2 (night) +1 (rain) +1 (tired) for 8 seconds driving distance.

SmartMotorist.com recommends doubling the time to 6 for adverse conditions and tripling it to 9 seconds for blinding rain, heavy fog, blizzard, and similar very adverse conditions. Of course for "very adverse" you might also consider pulling off the road and waiting.

Bottom Line

The distance needed to stop your car consists of two parts.

First is the distance your car travels while you notice the problem and the moment you finalize your decision and actually start to push the brake pedal.(your reaction time, 1.5 seconds on average if alert).

Second is the distance that brakes need to stop your car - actual stopping distance. This is the reason for more distance time in rain & snow. It takes longer to for the brakes to for the car to stop.

Also realize that it takes longer for heavy vehicles to stop. If a truck is tailgating you, you might be able to brake quickly enough to avoid a collision in front but the truck behind will run right over you. Don't let anyone bigger than you sit on your tail. Get out of the way.