When the American Automobile Association (AAA) withdrew from auto racing after the 1955 season, citing the Le Mans disaster and the death of Bill Vukovich at Indianapolis as contributing factors, both the SCCA and NASCAR were mentioned as its potential successor. Ultimately, USAC was formed by Indianapolis Motor Speedway owner Tony Hulman. It became the arbiter of rules, car design, and other matters for what it termed championship auto racing, the highest level of USAC racing. For a while there was a separate series of specifications for championship cars designed to be run on dirt, rather than paved, tracks.