Testing Vehicle Stopping Distance
Let's set up a typical braking test considering the factors we discussed in the previous section. For this test, we'll assume the vehicle is in good working order. Let's also assume the road is dry asphalt and in good condition. Mark a beginning point and physically measure the distance from that point to the vehicle each time. Now let's get down to business.
If your vehicle has an anti-lock brake system (ABS), conduct the test with it both on and off. Typically auto manufacturers conduct braking tests at 60 mph (96 kph). We'll do the same. Find a closed area void of traffic and obstructions. Once you get the vehicle up to the test speed, hit your brakes. Without anti-lock brakes, you can easily lock up the front tires and end up skidding, which can easily translate into loss of control and even a spin. Your goal is to hit the brakes as hard as you can until just before the tires start to skid. Keep two hands on the steering wheel and avoid overcorrecting if the rear of the car wants to come around. Conduct this test a few times to get the feel for your braking system.
Next, turn on the ABS and conduct the test again. With the ABS on, the car will feel different when you hit the brake. It's because the ABS pumps the brakes for you to the point where the tires are on the verge of losing traction. Sensors use feedback to dictate how much brake to use to stop the car as quickly as possible while avoiding tire skid. Some antilock systems even have a brake assist that takes over from the driver and applies the most amount of stopping power available [source: Edmunds].
Each driver has different abilities. Some have better reflexes than others; some are more experienced. The best thing you can do is give yourself room between your car and the vehicle in front of you and pay close attention when you drive. A good rule of thumb is a three to four second gap. Add more distance if the road is wet. You can figure this out by counting the time it takes for you and the vehicle ahead of you to pass a certain point on the road.
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- Helperin, Joanne; Memmer, Scott. Edmunds. "Keep Your (Braking) Distance: More Than Just Slowing Do." Nov. 23, 2000. (Oct. 19, 2010)http://www.edmunds.com/ownership/driving/articles/43810/article.html
- Jones & Childers. Contemporary College Physics, 3rd ed. "The Friction of Automobile Tires." 2001. (Oct. 20, 2010)http://www.physics.sc.edu/~rjones/phys101/tirefriction.html
- U.S. Department of Transportation: National Highway Transportation Safety Administration. "Brake Testing Methodology Study - Driver Effects Testing." March 1999. (Oct. 20, 2010)http://www.nhtsa.gov/DOT/NHTSA/NRD/Multimedia/PDFs/VRTC/ca/capubs/braketst.pdf
- Walt Disney World. "Test Track." (Oct. 20, 2010)http://disneyworld.disney.go.com/parks/epcot/attractions/test-track/