The age of jumbo jets and supersonic aircraft begins in the 1970s. These new aircraft will be considerably more expensive and capable of carrying many more passengers than the aircraft they replace. New methods for rating, predicting, and alleviating the slipperiness of airport runways are required to reduce the possibility of costly and even catastrophic accidents occurring to these and other aircraft on slippery runways.For the past year, the USAF and NASA have been conducting a cooperative runway research program on runways in the United States and Europe. The slipperiness of over 40 runways having different surface treatments has been rated under dry, wet, slush, snow, and ice conditions by means of an instrumented four-engine jet transport and an instrumented automobile.It is shown that measurement of the stopping distance of a diagonal-braked automobile provides a meaningful measure of the slipperiness of a wet runway and permits accurate prediction of the stopping distance of an aircraft, as well as realistic calculation of crosswind limitations. It is also shown that stopping distance on a wet runway can be considerably improved either by grooving the runway or by use of a porous surface course.