A growing number of private off-road dirt-racing parks are raising dust in places like Pettigrew, Combs, Mulberry, Fort Smith and Harrison. In mid-May more than 330 national and international vintage motocross racers swarmed the newest track, Mill Creek Motosports Park south of Combs in Madison County to compete in an American Historic Racing Motorcycle Association event. Private 4-and-2-wheel dirt-racing parks, which go mostly unregulated in Arkansas, attract new business to rural districts. But some are raising concerns about environmental impacts and noise.