Rallycross simulates the type of driving done in performance rallies but is essentially autocross on dirt or grass with autocross-style safety parameters. It is done in cars usually classed as FWD, RWD or AWD and whether prepared or not. Usually a driver may do several consecutive laps, each separately timed, and hitting a pylon adds time penalties. Sometimes a worst lap may be thrown out. Some events may offer a driver two sequences of laps. Helmets are required, and generally only closed (hardtop) cars are permitted. Two or more drivers may share a car. There is a national championship, most recently held in Tulsa, Okla.