Since off-road cycling began, mountain bike trail designs have the lengths, grades (the slope of the land), terrain and obstacles that appeal to different cyclists' interests. Designers build trails according to the skill of the riders who will use them. Trail designs around the world appeal to those looking for many different types of outdoor adventures.
A mountain bike trail aimed at a variety of riders should balance the technical challenge with easier-to-ride areas. Trail designs vary in width based on their intended use. Single-track trails are narrow, inaccessible to vehicles and horses, and sometimes they're used by hikers. Double-track trails are wide enough for two cyclists side-by-side.
To help riders determine if their skills match the trail, the International Mountain Bicycling Association (IMBA) established a Trail Difficulty Rating System. The ratings are similar to those you'd see worldwide for downhill skiing, including the famous black diamond ratings for the most challenging trails. Trails are rated on width, tread surface, average grade, maximum grade, natural obstacles and technical trail features [source: IMBA].
Competition trails target adventure sports enthusiasts, and they're designed according to the rules of the sport. The International Cycling Union (UCI) is a long-standing non-profit organization for maintaining international standards in competitive cycling. UCI trail requirements are listed in detail in their official rules, including the requirements unique to events such as cross-country, downhill and mountain cross.
Trail builders include groups of mountain biking enthusiasts as well as professional construction workers. IMBA members volunteer to help in trail building worldwide. IMBA maintains a list of the "10 Most Common Trailbuilding Mistakes" to help avoid the mistakes of past builders. When governments and non-profit groups are looking for paid contractors to build trails, they can look to organizations like the Professional Trailbuilders Association (PTBA) to find contractors who specialize in trails.