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Trail Construction and Maintenance Notebook

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Trail Corridor

The trail corridor is a zone that includes the trail tread and the area above and to the sides of it. Trail standards typically define the edges of this area as the "clearing limits." Vegetation and other obstacles, such as boulders, are trimmed back or removed from this area to make it possible to ride or walk on the tread (Figure 5).

The dimensions of the corridor are determined by the needs of the target user and trail difficulty level. For example, in the Northern Rockies, trail corridors for traditional packstock are cleared 2.5 m (8 ft) wide and 3 m (10 ft) high. Hiker trails are cleared 2 m (6 ft) wide and 2.5 m (8 ft) high. Check with your local trail manager to determine the appropriate dimensions for each of your trails.

Graphic of trail structure terminology.
Figure 5--Terms describing the trail corridor. Often there
will be detailed dimensions you need to know.

Clearing and Brushing

Working to wipe out your trail is no less than that great nuclear furnace in the sky--Old Sol, the sun. Working in cahoots with the mad scientist, Dr. Photosynthesis, the sun works an alchemy that converts dirt and water into a gravity-defying artifice called a plant. Seasoned trail workers will attest to the singular will and incredible power of plants. No sooner is a trail corridor cleared of plants than they begin a rush toward this new avenue of sunlight.

A significant threat to trail integrity comes from plants growing into trail corridors, or from trees falling across them. Brush is a major culprit. Other encroaching plants such as thistles or dense ferns may make travel unpleasant or even completely hide the trail. If people have trouble traveling your tread, they'll move over, usually along the lower edge, or make their own "volunteer" trail. Cut this veggie stuff out! (Figure 6).

Photo of a trail that is not cleared of vegetation.
Figure 6--Vegetation before trail clearing. Each type
of trail has its own requirements for clearing.

In level terrain the corridor is cleared an equal distance on either side of the tread centerline. Using the hiking trail example, this means that the corridor is cleared for a distance of 1 m (3 ft) either side of center. Within 300 mm (1 ft) of the edge of the tread, plant material and debris should be cleared all the way to the ground. Farther than 500 mm (1.5 ft) from the trail edge, plants do not have to be cleared unless they are taller than 500 mm or so. Fallen logs usually are removed to the clearing limit.

On moderate to steep side slopes, a different strategy is often useful. Travel along the lower (outer) edge of the tread is a significant cause of tread failure. You can use trailside material to help hold traffic to the center of the tread. A downed log cut nearly flush with the downhill edge of the trail will encourage travelers to move up to avoid it. Rocks, limbed trees, and the like can all be left near the lower edge of the tread to guide traffic back to the center (Figure 7).

Photo of a trail supported by rocks and logs.
Figure 7--Rocks and logs help to keep the trailing place.
And remember that this is a path through nature,
not a monument to Attila the Hun.

The key is to make sure that the guide material will not interfere with travel on the center of the tread. For example, bikers need enough room for pedals or foot pegs to clear both the backslope and the guide structures.

On the uphill side of the trail, cut and remove material for a greater distance from centerline. For instance, on slopes steeper than 50 percent you may want to cut downed logs or protruding branches 2 m (6.5 ft) horizontal distance or more from the centerline. This is particularly true if you're dealing with packstock as they tend to shy away from objects at the level of their heads.

Using this "movable corridor" takes some thought. Recognize that this may be a difficult decision for inexperienced crews. Continue to revisit the basic reasons for clearing a corridor and the consequences of taking or leaving material.

Finally, remember that the "scorched earth" look created by a corridor with straight edges is not very pleasing to the eye. Work with natural vegetation patterns to "feather" or meander the edges of your clearing work so they don't have such a severe appearance. Cut intruding brush back at the base of the plant rather than in midair at the clearing limit boundary. Cut all plant stems close to the ground. Scatter the resulting debris as far as practical. Toss stems and branches so the cut end lies away from the trail (they'll sail farther through brush as well). Don't windrow the debris unless you really and truly commit to burn or otherwise remove it (and do this out of sight of the trail). Rubbing the cut ends of logs or stumps with soil will reduce the brightness of a fresh saw cut. In especially sensitive areas, cut stumps flush with the ground and cover with dirt, pine needles, or moss. Rub dirt on stobs or bury them. Remember...this is America the Beautiful!

Some trails may have to be brushed several times a year. Some once every few years. Doing a little corridor maintenance when it is needed is a lot easier than waiting until plants cause expensive problems. Jump on potential problem areas before they become real problems.

Removing Trees

Trees growing within the corridor should usually be removed. Remember that those cute little seedlings will eventually grow into pack-snagging adolescent trees. They are a lot easier to pull up by the roots when they are small than they are to lop when they grow up.

Prune limbs close to the tree trunk. For a clean cut, make a shallow undercut first, then follow with the top cut. This prevents the limb from peeling bark off the tree as it falls. Do not use an ax for pruning.

If over half of the tree needs pruning, it is usually better to cut it down instead. Cut trees off at ground level and do not leave pointed stobs (Figure 8).

Drawing of wrongly pruned trees.
Figure 8--These trees should have been
removed rather than pruned.

"Logging out" a trail means cutting away trees that have fallen across it. It can be quite hazardous. The size of the trees you are dealing with, restrictions on motorized equipment, and your skill and training will determine whether chain saws, crosscut saws, bow saws, or axes are used. Safety first!

You need training to operate power saws and crosscut saws. Your training, experience, and, in some cases, level of certification can allow you to buck trees already on the ground or to undertake the more advanced (and hazardous) business of felling standing trees. Be sure you are properly trained and certified before cutting either standing or fallen trees. Remember that using an ax exposes you to similar hazards.

Some trees may be more safely felled by blasting. Check with a certified blaster to learn where blasting is a feasible alternative.

Removing fallen trees is a thinking person's game. The required training will help you think through problems, so we won't relate the details here.

Cut the log out as wide as your normal clearing limits on the uphill side, and out of the "clearing zone" but closer to the trail on the downhill side. Roll the log pieces off the trail and outside the clearing limits on the downhill side. Never leave them across ditches or waterbar outflows. If you leave logs on the uphill side of the trail, turn or bed them so they won't roll or slide onto the trail.

Sometimes you'll find a fallen tree lying parallel with the trail. If the trunk of the tree is not within the clearing limits and you decide to leave it in place, prune the limbs flush with the trunk.

It is hard to decide whether or not to remove "leaners," trees that have not fallen but are leaning across the trail. If the leaner is within the trail clearing zone, it should be removed. Beyond that, it is a matter of discretion whether a leaner needs to be cut. The amount of use on the trail, the time until the trail is maintained again, the soundness of the tree, and the potential hazard the leaner is creating all need to be considered in your decision. Felling a leaner, especially one that is hung up in other trees, can be very hazardous. Only highly qualified sawyers should do it (Figure 9). Blasting is another way to safely remove leaners.

Walk away from it!
Figure 9--If you are uncomfortable with your ability
to safely cut a tree due to the hazards or your
lack of experience, walk away from it.

Felling standing trees (including snags) is statistically one of the most dangerous activities a trail worker can engage in. Simply put, do not even consider felling trees unless you have been formally trained and certified. Bringing in a trained sawyer is cheaper than bringing in a coroner.

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Updated: 4/14/2014
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