About 22 percent of all loaded tractor-trailers exceed State weight limits, and the percentage ranges as high as 81 percent for other types of trucks. This is significant because a five-axle, tractor-trailer loaded to the 80,000-pound Federal limit, has the same impact on an interstate highway as 9,600 automobiles. In addition, as truck axle weights increase, pavement damage increases an at even faster rate. For example, while a truck axle carrying 18,000 pounds is only 9 times heavier than a 2,000-pound automobile axle, it does 5,000 times more damage. Although excessive truck weight is a major contributor to highway wear, Federal weight limits do not apply to at least 95 percent of the Federal-aid highways. In addition, a grandfather clause in existence since origination of Federal weight limits in 1956 stipulates that truck weights which were permissible in individual States at that time can remain in effect indefinitely. As a result, at least 20 States have limits higher than Federal weight limits in at least one weight category on their interstate highways. The Federal Highway Administration has not provided the guidance and assistance necessary to improve State weight enforcement, and the level of effort committed to weight enforcement varies greatly from State to State. Safety issues should not be ignored. The public is being exposed to increasing vehicle size and weight differentials, as automobiles get smaller and lighter while trucks become larger and heavier. The Secretary of the Department of Transportation should direct the Federal Highway Administratior to develop, in cooperation with the States, a model State weight enforcement program.