Mathematics and Driving (who says we wouldn’t use this stuff later?)
As the warm weather and black flies descend upon us, we all anxiously await that exciting day when the kids are off school for the summer. There are vacations, beach trips, yard work and assorted activities. The police department’s calls for service change to more outdoor-related calls, including collisions, motor vehicle complaints and drunk driving, amongst others.The point of this letter is to talk a little about driving and safety…and math.

In school, I was best described a “history nerd” with little interest in arithmetic. I did it, but didn’t always like it. After 20+ years of investigating motor vehicle collisions, I have to admit that math has been an integral piece of these investigations.

For example, when talking about driving, we all use “miles per hour” and really do not think much more about it. The number on the speed limit signs and on our speedometers became “just a number” sometime in our life. But a closer look reveals something tangible (or it should).

Example: 65 m.p.h. = 95.3 feet per second.

Find something 95 feet away from you and consider moving that distance in a second.

Now, let us consider reaction time and distance. If you are a typical driver, but you are alert and watching the road, a survey from NHTSA reports that it takes you 1.5 seconds to realize something has occurred in front of you and you need to react. So, you are traveling on the Interstate and see a moose, deer, etc. Your car will travel 143 feet before you can even put your foot on the brake. This does not include the extra time you would need to add because you are on your cellphone, changing a radio station, finding that particular song on your MP3 player, or applying makeup.

Next, let’s say the road is dry and fairly warm. All of your brakes are in excellent condition. At the 65 MPH speed limt it will take approximately 188 feet to stop.

So, to summarize your issue at hand, you are traveling at 65 MPH, you see a problem in the road. You apply the brakes. If the object is less than 331 feet away, your vehicle will strike it. That is more than a football field including the end zones. The only option you had was to take an evasive action and steer around the obstruction if possible. If you were traveling at 75 mph under the same circumstances, the total distance covered increases to 415 feet.

Oh yea, another thing…seat belts. As you probably are well aware, New Hampshire is the only state that does not require adults to wear a restraint while driving on our highways. I will not use this forum to preach or politicize this issue, but would like you to understand that everything in your car will travel at whatever speed the car was doing at impact in an opposite direction, including human beings. Those airbags that many of you have in your car are designed to deploy upon impact and are further designed for you to be in your seatbelt in a controlled location in the cab of your vehicle. If you are not “tied in”, the air bag can actually move you into harm’s way. The bag typically deploys at about 150-200 mph but is already deflating by the time the body strikes it. If you aren’t restrained, the body can make contact too early and get “punched” by the inflating air bag.

Air bags used in conjunction with seatbelts save saves. Actually the combination saves 26% more drivers than belts alone. (Insurance Institute for Highway Safety. “Airbag Statistics.” 7 October 1998) According to NHTSA research, 75 percent of all traffic deaths and injuries occur within 25 miles of victims’ homes, at speeds of less than 40 miles per hour (Remember, that’s 58.6 feet per second). Being thrown against a dashboard in a 30 mile-per-hour crash is like striking the ground after falling from a third-floor window. Even a crash at only 12 miles per hour can be fatal.

So, drive safely. I hope you all enjoy that drive to the beach, or even to the local swimming hole. Remember your math!

Chief Warn

May 31, 2011