I've never heard of any involvement at all by auto companies. What source suggested there was?

Superhighways were the response of the highway engineering profession to the problems of growing auto traffic and the appalling crash rate when autos were used on the streets and roads laid out in previous centuries. The concept of a limited-access, grade-separated, multilane facility was demonstrated in the 1930s with short urban stretches in and near New York City and Chicago's Lake Shore Drive. Several similar facilities were in place around the country by 1940, when the Pennsylvania Turnpike demonstrated the demand for cross-country superhighways as well. By 1957, about 1.5 percent of "federal-aid" and toll highways were already superhighways; today—though the statistics are not strictly comparable—about 19 percent are.

Planning for such facilities continued through the war years, and state highway departments began building as soon after the war as they could, using whatever funds they could scrape together. In several states, toll financing provided the way to get such highways built. A federal-aid financing program for a new network of superhighways took three years of congressional wrangling discussed in this previous thread before finally resulting in the 1956 Interstate program.

As the Interstate program became law, Ford put out a widely distributed booklet, "Freedom of the American Road," that touted the safety and efficiency of the new highways. From the date, it seems unlikely to have appeared in time to influence congressional debate. Undoubtedly General Motors and the insurance industry did similar public relations booklets and films, but I've never heard them mentioned in discussions of the legislation.

I like Earl Swift’s The Big Roads as the most readable history of the Interstates, but Mark Rose's Interstate: Express Highway Politics 1939-1989 is the more scholarly source on the congressional machinations. A more recent book by Joseph DiMento and Cliff Ellis, Changing Lanes: Visions and Histories of Urban Freeways, recounts the history of how traffic engineers and city planners wrangled with this new force reshaping the city.