The unknown dangers of excessive speed
By Steve Wallace, Times Colonist, May 31st 2013
Most drivers have no idea how far it takes to stop their vehicle in an emergency. Drivers who consistently exceed the posted speed limit are particularly at risk for a significant and damaging crash.
Here is a test of your own estimate of excessive-speed differential and stopping distance.
Two vehicles going the same direction, in the same lane, enter a narrow tunnel. The driver following the lead car chooses to pass, despite the inherent risks. The lead car is travelling at the speed limit of 80 km/h. The vehicle passing the lead car reaches a speed of 110 km/h at the exact time that the front bumpers of each vehicle are exactly even. At that very instant both drivers see the end of the tunnel is completely blocked by a large loaded transport vehicle. Each driver slams on the brakes in an effort to stop before hitting the truck. Stopping is their only hope of avoiding a crash. The driver going 80 km/h stops just in time to avoid a crash. The driver going 110 km/h crashes. My question is a simple one. How fast do you think the speeding driver hits the obstacle blocking the tunnel exit?
For the purposes of this example, let us assume the drivers are twins with equal reaction time, the road surface is the same, the vehicles are of equal weight with comparable brakes and tires. All things being equal, the passing vehicle crashes at a speed of 88 km/h! Are you shocked? I was even more shocked as a driving instructor-candidate some 30 years ago, when I experienced this very scenario at the Boundary Bay Airport driver-training course.
The 30 km/h speed differential can be lethal in a typical crash. Drivers who speed excessively are usually not aware of the inherent dangers of that very excessive speed.
The laws of physics will trump the laws of man every time. Most people who are intent on speeding are all too aware of the possible police presence on our roads. What they are not so aware of is the drastically increased chance of being killed or killing someone else because of a thoughtless, selfish, inconsiderate driving behaviour. A traffic ticket for such potentially destructive behaviour should be the least of their worries.
Braking distance increases by a square proportion with increased speed. When a driver doubles his or her speed, the braking distance increases by four times, not twice. An increase of three times the speed will yield a nine-times increase in stopping distance, not three times.
Considering the tunnel example, together with the braking-distance information, is it any wonder that the most common roadway crash is the rear-end collision? Even under good driving conditions, most drivers do not follow the three-second rule of following distance. The two-second rule is now simply not enough space, when one considers the variety of vehicles on the road today, from miniature gas misers to super-tanker trucks, scooters and motorcycles.
Every driver should be aware of the distance necessary to safely stop a vehicle in an emergency. Doing a panic stop is the only way to truly know this distance. Every driver should do a panic-stop drill at least once a year under controlled circumstances, in order to appreciate the square-proportion principle of braking distance. Every good driving school does this drill. Sadly, the vast majority of drivers never do the drill and are ill-prepared when actual driving circumstances require it.
Steve Wallace is the owner of Joan Wallace Driving School on Vancouver Island and in the Central Interior of B.C. He is the former Western Canadian vice-president of the Driving Schools Association of the Americas and a registered B.C. teacher.