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. Drafting is of far less strategic importance than in road racing, though it can still be employed in paved sections or extremely windy conditions. Instead, tactics are chiefly focused on line choice, pacing strategy, passing technique, and racers' ability to identify and exploit sections of the course that are conducive to attacking or recovery. Each section of the course typically lasts no longer than a handful of seconds. For example, long climbs are avoided in favour of short, sharp inclines. Sections are generally linked together, or long straights broken up, with tight corners. This not only allows a standard length course to fit in a relatively small area, but also forces competitors to constantly change speed and effort. Accelerating out of corners, then having to decelerate for the next before accelerating again is a common theme. Obstacles that force a rider to dismount and run with their bike or to "bunny hop" include banks too steep to ride up, steps, sand pits and plank barriers. Besides the start/finish area, these obstacles may be placed anywhere on the course that the race director desires. Several race directors have tried to limit bunny hopping for safety reasons by placing barriers in pairs or in triple (although under UCI rule no more than two barriers can appear in succession). The regulation height for a barrier is 40 cm although this is treated as a maximum at smaller events. Plank barriers seem to be more common in the US than in Europe, and UCI