On a blazing hot morning last week, 75 men and women of the highway - bus drivers, truckers and van operators - convened at a nondescript office building in Little Rock, Ark., to be trained as terrorist hunters. The Department of Homeland Security this year gave $19.3 million to the American Trucking Associations, which is based in Alexandria, Va., to recruit a volunteer "army" called Highway Watch. So far, 10,000 truckers have signed on to become amateur sleuths. Over the next year, the goal is to add tollbooth workers, rest-stop employees and construction crews, creating a corps of 400,000 people drawn from every state.