beyond the peak, then release the brakes until wheel slip is reduced and then apply them again. This pressure/release/pressure cycle happens many times per second so the amount of braking force is as great as possible. It continues until traction is restored or the driver releases the brake pedal. IV. Testing/Findings/Conclusion The National Highway Traffic Safety Administration has conducted a series of tests to evaluate the performance of antilock brakes under conditions that have been encountered in actual accidents. These tests focused on split friction surfaces. In these instances, the two right wheels of a car would be on one surface, as when the tires have gone off the edge of the road and are now on wet grass. The left tires are still on the paved road surface, such as wet asphalt. There is a considerable difference in the effective drag factors between the two surfaces. With normal brakes, the right side wheels would be expected to lock up first, causing the vehicle to spin counter-clockwise. With anti-locks engaged, all four wheels should continue to rotate allowing the driver to bring the car to a safe stop in a relatively straight line. The test vehicles all came to a halt in a straight line with the anti-locks engaged. When they were turned off and a panic stop was attempted, they all rotated 45 degrees before coming to a stop. During one series of tests, using dry asphalt on one set of wheels and loose gravel on the other, the total stopping distances increased, some dramatically. In one instance, the test vehicle required 62 percent more stopping distance, and 74 percent in the other. These results were expected, as antilock brakes are less effective on loose gravel than standard brakes. The actual reduction in stopping distance when a vehicle is equipped with ABS is not that significant under most circumstan...
