4X4Explore.com - 4WD Road Difficulty Ratings

Definitions of measurement:

Grade - The rise over run, or angle, of the 4WD roadbed measured on an 6 foot span laid parallel or in line with the roadbed.
Pitch - The rise over run, or angle, of the 4WD roadbed measured on a 6 foot span laid perpendicular or across the roadbed.
Width - The physical width of the 4WD roadbed at the narrowest section.
Surface - The material and physical description of the 4WD roadbed.
Obstacle - The measurement of the diameter, height, length, depth, of an obstacle in the 4WD roadbed.

Name	Easy	Moderate	Difficult	Extreme
Difficulty	Easy 1 - 4	Moderate 5 - 7	Difficult 8 - 9	Extreme 10
Grade	20% to 30% (11º to 17º)	30% to 40% (17º to 22º)	40% to 50% (22º to 27º)	50% or more (27º to ??)
Pitch	10% to 20% (6º to 11º)	20% to 30% (11º to 17º)	30% to 40% (17º to 22º)	40% (22º)
Width	12ft.	10ft. to 12ft.	8ft. to 10ft.	6ft. to 8ft.
Surface	Improved, gravel, blading, contouring	Natural, some contouring	Natural, some fill	Natural
Obstacle	Rocks - to 9" Steps - to 8" Water - to 6" deep Mud - to 4" deep Sand - to 4" deep	Rocks - 9 to 14" Steps - 8 to 16" Water - 6 to 12" deep Mud - 4 to 8" deep Sand - 4 to 10" deep	Rocks - 14 to 20" Steps - 16 to 30" Water - 12 to 24" deep Mud - 8 to 16" deep Sand - 10 to 20" deep	Rocks - 20" or more Steps - 30" or more Water - 24" or more Mud - 16" or more Sand - 20" or more

Other considerations are the number of occurrences of a characteristic that are required for a 4WD road to receive a particular difficulty rating. Typically only one occurrence of a specific level of obstacle gives the 4WD road that difficulty rating. This is to insure that recreationists are not attempting a challenge that is beyond their ability.