, the International Mountain Bicycling Association, has many resources available.
The following article
describing IMBA's Trail Difficulty Rating System is taken directly from their book Trail Solutions: IMBA's Guide to Building Sweet Singletrack
. This 272-page book combines cutting-edge trail building techniques with proven fundamentals in a colorful, easy-to-read format. The book is available for purchase from IMBA.
The IMBA Trail Difficulty Rating System is a basic method used to categorize the relative technical difficulty of recreation trails. The IMBA Trail Difficulty Rating System can:
* Help trail users make informed decisions
* Encourage visitors to use trails that match their skill level
* Manage risk and minimize injuries
* Improve the outdoor experience for a wide variety of visitors
* Aid in the planning of trails and trail systems
This system was adapted from the International Trail Marking System used at ski areas throughout the world. Many trail networks use this type of system, most notably resort-based mountain biking trail networks. The system best applies to mountain bikers, but is also applicable to other visitors such as hikers and equestrians. These criteria should be combined with personal judgment and trail-user input to reach the final rating.
Read the full article here: http://www.imba.com/resources/trail_building/itn_17_4_trail_difficulty.html