Simplify the following text for a Grade 6 native English-speaking person.
Original: In the United States some top-level open wheel events are held on ovals , of both short track and superspeedway variety , with an emphasis being placed more on speed and endurance than the manueverability inherently required by road and street course events .
Simplified: In the United States some top-level open wheel events are held on ovals , both short track and superspeedways .