When a rider crashes, track marshals up the track from the incident wave yellow flags, prohibiting overtaking in that area; one corner farther up the track, a stationary yellow flag is shown. If a fallen rider cannot be evacuated safely from the track, the race is red-flagged. Motorcycle crashes are usually one of two types: lowside, when the bike loses either front or rear tire grip and slides out on the "low" side, and the more dangerous highside, when the tires do not completely slide out, but instead grip the track surface, flipping the bike over to the "high side", usually catapulting the rider over the top. Increased use of traction control has made highsides much less frequent.