The moab trail rating system has been changed from the old 1-4+ rating system to a 1-10 rating system, similar to Colorado, though it seems a little harder. Below is an approximate description of the new ratings. The actual descriptions are on Red Rock 4 wheelers website, which is copywrited, so this is my interpretation of their ratings with my experience thrown into the mix.
Rating:1
County dirt road. The road is maintained. Most 2wd and all 4wd vehicles can drive these trails.
Rating:2
County dirt road. Some maintenance after rain or snow, but high clearance is recommended. Lower gearing may be needed. May have some ruts, smaller rocks, mild hills. Should be passable by all 4wd vehicles.
Rating:3
The road is hardly maintained, and the surface can be dirt, rock or sand. There can be ruts and holes. 4 wheel drive is recommended as is high clearance. Depending on the trail, it can be very difficult if wet.
Rating:4
Rutted and/or rocky road. Steps up to 12". 4WD under most conditions. The surface can be any combination of slickrock, dirt, sand or rocks. You should have high clearance. You may encounter water, mud, washes or eroded sections of trail. You should have good driving skills. Fairly steep slickrock sections may be encountered, but should be passable by most 4wd vehicles with low range.
Rating:5
Rutted and/or rocky road that can have long slickrock sections. Rocks or steps up to 14" and water crossings up to 12" with possible mud. 4WD required. Taller tires and traction aids are recommended as are good driving skills. Body damage is possible and things can be broken if care isn't taken.
Rating:6
Quite rocky or deep ruts, steps up to 24" with lots of slickrock. Mud is possible and water can be deeper than 12". Tall tires and traction aids are recommended as is good articulation and very good driving skills. Good approach and departure angles are needed as hills can be steep. Damage or breakage is possible. Rolling is possible on certain trails, though not likely.
Rating:7
Any trail surface is possible, but it will probably be long expanses of slickrock. The trail can have steep hills and many steps taller than 24". Recommended for experienced drivers. Vehicles should have tall tires and locker(s) and very good ground clearance. A winch could be helpful. Damage is possible and there are opportunities for the vehicle to roll if care is not taken.
Rating:8
Heavily modified vehicles and front and rear lockers are needed, and a winch is helpful. Fairly large rocks, ledges and steps are probable, Rolling is possible, and body/mechanical damage likely. Steep hills are possible.
Excellent driving skills needed.
Rating:9
These trails are even more extreme, with common rollovers and very likely vehicle damage. Requires front and rear lockers and a winch. Best for buggies or the most modified stock vehicles only. Breakage is likely. Very large rocks, steps and ledges possible as well as very steep sections.
Rating:10
The hardest of the hard! Buggies only on these trails. Very large rocks, ledges and steep climbs/descents. Rolling is very probable and breakage of some vehicles almost guaranteed. If you have to ask how hard it is, you don't belong on it.

