Races usually consist of many laps over a short course, ending when a time limit is reached rather than after a specific number of laps or certain distance; the typical length for senior events is one hour, with 30 and 45 minute races for lower categories being the norm. Generally each lap is around 2.5-3.5 km and is 90% rideable. Races run under UCI rules must have courses that are always at least 3 m wide to encourage passing at any opportunity, but sections of singletrack are common for small races in the US and Great Britain. A variety of terrain is typical, ranging from roads to paths with short steep climbs, off camber sections, many corners and, a defining feature, sections where the rider may need, or would be best advised to dismount and run while carrying the bike. Under-tire conditions include asphalt, hardpack dirt, grass, mud and sand. In comparison to cross-country mountain bike events, terrain is smoother. Less emphasis is put on negotiating rough or even rocky ground with more stress on increased speed and negotiating different types of technical challenges.