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Highway Numbering
Highway Numbering in California

Forest Routes

The forest routes are part of a vast system of roads that provide access to national forest lands. They're used in logging, mineral extraction, livestock grazing, etc. They provide access to campgrounds, hiking trails, and other recreational resources, as well as being about the only access to a good deal of private land. The particular numbering system varies quite a bit from national forest to national forest. All route numbers are shown on the Motor Vehicle Use Map, which also shows the level of maintenance of the route.

Forest Highways

There is a general hierarchy of routes in a national forest. The first level is a "Forest Highway," which are are generally maintained to be accessible to all vehicles. Definitely gravelled and often paved, Forest Highways are often not signed as such when they are designated along a state or US route. These are generally routes that are of some significance regarding the outside world, rather than just within the forest.

According to the Code of Federal Regulations, Forest Highways are designated by number and name. Numbering is consecutive within each state, and no number is to be used more than once in each state. Other road numbering systems (i.e. those used outside the forest) are disregarded in numbering the Forest Highway routes.
(CFR Title 23 §660.205)

Forest Routes

There is a second class of forest routes that are maintained to low-clearance standards for passenger cars (i.e. you might not be able to travel at highway speeds, but with a little care, you should be able to get most vehicles up the things. These normally do not have formal shields, but have numbers are often posted horizontally on signs.

There are basically five levels of maintenance of forest routes generally open to the public:

  1. Maintenance Level 5: Roads that provide a high degree of user comfort and convenience. Normally double lane, paved facilities, or aggregate surface with dust abatement. This is the highest standard of maintenance.
  2. Maintenance Level 4: Roads that provide a moderate degree of user comfort and convenience at moderate speeds. Most are double lane, and aggregate surfaced. Some may be single lane. Some may be dust abated.
  3. Maintenance Level 3: Roads open and maintained for travel by a prudent driver in a standard passenger car. User comfort and convenience are not considered priorities. Typically low speed, single lane with turnouts and native or aggregate surfacing.
  4. Maintenance Level 2: Roads open for use by high-clearance vehicles. Passenger car traffic is discouraged. Traffic is minor administrative, permitted or dispersed recreation. Non traffic generated maintenance is minimal.
  5. Maintenance Level 1: These roads are closed. Some intermittent use may be authorized. When closed, they must be physically closed with barricades, berms, gates, or other closure devices. Closures must exceed one year. When open, it may be maintained at any other level. When closed to vehicular traffic, they may be suitable and used for nonmotorized uses, with custodial maintenance.

In the Angeles National Forest, the numbers have the form 3N02. These routes are often trunk routes for the forest highways.

The secondary roads often connect to still smaller roads, which are "maintained" for high-clearance vehicles only. These will generally lead from the trunk roads to timber sales, lakes, meadows, and random locations that just happen to have roads to them. There are a lot of these on the maps, though they are not often marked on the ground, although you may occasionally find a vertical string of numbers on a 3 inch wide fiberglass post.

Although not a topic of this website, there are sites that address Forest Road numbering. For example, explores the numbering of Forest Roads and Trails in the Angeles National Forest. This site notes that:

Over on AARoads, Tom Fearer noted: Forest Route numbers generally follow a convention based off the Township they originate in. All National Forests are charted in a Township and Range grid, in the case of the former they span 6 mile sectors. For roads like Forest Route 10 they also carry a Forest Road Number which denotes it's Township point of origin. Much of Forest Route 10 is internally numbered as Forest Road 6S10 denoting it's point of origin is in Township 6S of Sierra National Forest. Forest Service Roads are given numbers based off where what Township the north terminus is located in. Spur routes of a mainline Forest Route carry a letter designation at the end hence why Beasore Loop is signed is numbered Forest Road 6S10X. Most National Forests tend to place two digit route shields on Forest Routes which are suited to travel by conventional vehicles which includes run of the mill cars. In the case of the Sierra Vista Scenic Byway while there are rough roads in it's alignment all of them can be traversed by a normal low clearance car.
(Source: Tom Fearer (Max Rockatansky) on AARoads, "Re: Sierra Vista Scenic Byway; Sierra National Forest Routes 10, 7 and 81", 8/7/2019)

As noted, the site gives much more information on this. This numbering system appears to be used in other national forests as well, although sometimes the posted route number is only a portion of the full route number, or is a different number entirely.

For example, some forest roads in the Sierra National Forest only post the last two digits of the route number, making Forest Route 6S10 into Forest Route 10. A few others even post different numbers than the original number: For example, Forest Route 13S09 in the Sequoia National Forest is posted as Forest Route 30.
(Source: Tom Fearer on FB, 7/28/2019)

(Much of the information on Forest Highways was provided in an m.t.r posting by Sam Smith.)

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