Calculate the skid speed by multiplying the drag factor times the braking efficiency times the skid distance times 30 and taking the square root of the result. For example, if the car skidded 120.5 feet on a road with a drag factor of 0.5 and left four skid marks, the car was going about 42.51 mph.

a. A vehicle leaves 40′ of skid marks before coming to rest- the original speed is about 30 mph for both drag factors.

1. Using the table, a skid mark of length 200 feet, implies a speed of 69 mph. Dek’s ‘rule of thumb’ gives a speed of 100 mph Mani’s ‘rule of thumb’ gives a speed of 80 mph. So Mani’s rule gives the best estimate.

dis the distance the car skidded (in feet). fis a special number (called the coefficient of friction) that depends on the road surface and road conditions. S = ~30d(I.O) (dry tar road). For a wet tar road, f is about 0.5, so the formula is S = ~ 30d(0.5) (wet tar road).

Driver Care – Know Your Stopping Distance

Example: velocity = 50 MPH. stopping distance = 5 squared = 25, add a zero = 250, divide by 2 = 125, sum 2*50 = 225 feet (the exact value can be calculated using the formula given below the diagram on the right).

When should you use the ‘two-second rule’? Explanation: In good conditions, the ‘two-second rule’ can be used to check the distance between your vehicle and the one in front. This technique works on roads carrying faster traffic. Choose a fixed object, such as a bridge, sign or tree.

This two seconds is the minimum for safe driving. If being followed closely by a large vehicle, increase your following distance from traffic ahead, so if you need to brake hard, you can do so more gradually, and thus avoid the unpleasant experience of being run over by the truck.

“Here’s the deal. Figure one car length for every ten miles an hour,” Barndt said. “So if you’re doing 55 miles an hour you should have six car lengths between you so that if something happens to the car in front of you, you have time to stop or react.”