A gravel road that is drivable by a 2WD vehicle in most conditions except in extreme weather conditions. This road will mostly be 2 lanes wide with guard rails in situations of steep drop offs.
A gravel road with some ruts and slight grades up to 15 degrees. This road is passable in a 2WD vehicle is good conditions but under some weather conditions may require 4WD.
A gravel road with some water crossing, Small rocks or holes, ruts and slight grades, up to 15 degrees. 4WD recommended but 2WD possible under good conditions and with adequate ground clearance and skill. No width problems for any normal vehicle. Vehicle passing spots frequently available if less than two vehicles wide.
Rutted and/or rocky road. No shelves but rocks to 9". Water crossings usually less than hub deep. Passable mud, and moderate grades, up to 15 degrees. Side hill moderate up to 15 degrees. 4WD required under most conditions.
Rutted and/or rocky road, small shelves. Rocks up to 12" and water crossings up to 12" with possible currents. Moderate grades to 15 degrees, 6" holes and off camber situations to 20 degrees. 4WD required.
Quite rocky or deep ruts, rock shelves up to 6 inches, rocks up to 12" and frequent. Water crossings may exceed hub depth with strong currents. Moderate grades to 20 degrees, sidehill situations may approach 30 degrees. 4WD required and second attempts may be required with stock vehicles. Caution may be required with wider vehicles.
Rocks frequent and large, up to 12" and may exceed hub height. Holes frequent or deep up to 12 inches in depth. Shelves to 9". Grades to 25 degrees and sidehill to 30 degrees. Water crossings to 18" and may have strong currents. 1-1/2 vehicles wide. 4WD required. Driver experience is required.
Large rocks and severe ruts. Rocks exceeding hub height frequent. Water crossings may exceed 30" in depth. Shelves to 12", steep grades to 25 degrees can be loose or rocky, off camber situations to 30 degrees. One vehicle wide and vehicle body damage possible. Driver experience and vehicle modifications are required.
Rocks over 15" in height. Frequent deep holes over 15". Shelves over 15". Over 30" water crossings with strong currents. Steep grades over 30 degrees, Sidehill over 30 degrees. A stock vehicle can expect significant damage. Experience essential, mechanical breakdown is likely, and a rollover is very probable. Extreme caution is recommended. Driver experience and vehicle modifications are required.
Severe conditions and extreme caution is recommended. Winching maybe required. The trail may be impassable by all but the extremely modified vehicles. Impassable under anything but ideal conditions. Vehicle damage is to be expected and personal injury is possible. Drivers need to exercise extreme caution at all times.