Stopping Your Vehicle In An Emergency

“Stopping Your Vehicle”

After this past winter we all know that it is different trying to stop your vehicle on dry roads as compared to a wet road or snowy road. But when you look at the actual figures of the stopping distances it is alarming! Lets take a look at what is going on when we have to make an emergency or sudden stop. Let’s say you’re driving along and suddenly a child runs out in front of you. The first thing that happens is you perceive the emergency. If you are unimpaired (not under the influence of drugs or alcohol, not fatigued and concentrating on driving) it takes 3/4 of a second to perceive that emergency. Then it takes another 3/4 of a second to get your foot off the gas and on to the brake. During that 1 1/2 seconds your vehicle is still traveling at a constant speed and nothing is going on to stop you. Then depending on the road surface it will take a certain time and distance to stop.  When we have trucks with air brakes there is an added concern. There is an air brake lag time. If  the air brakes are working properly (all in alignment, no leaks etc.) the lag time is .4 of a second. It takes that lag time for the brakes to react to the air moving through the system. That lag time is almost incomprehensible. But the truck is still traveling at a constant speed.

To illustrate the stopping distance at different speeds on different road surfaces I put together the following chart. Note that while traveling on a wet road (raining) at 55 M.P.H.; it would take an unimpaired driver driving a vehicle with air brakes 6.7 seconds and 320 feet to stop. What does that really mean? A football field is 300 feet long; it would take over a football field to stop that truck! I present this information during my Defensive Driving Programs. Those in attendance are overwhelmed by this information. I then tell them, “it is not going to take that long to stop their vehicle. They are going to hit something long before that.”

Keep in mind the next time your driving, it may take you a long time and distance to stop a vehicle in an emergency situation. Being aware and prepared may save a life.

SpeedRoad SurfaceTime to Stopn(seconds)Distance to Stopn(feet)
30Dry3.61122
30Wet4.18134
30Wet Snow8.7234
55Dry5.03278
55Wet6.7320
55Wet Snow14.5656
70Dry5.9400
70Wet7.2467
70Wet Snow17.81,011

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