There is a real art to trail layout. Some basics can be taught, but the person locating the trail must develop an eye for laying a trail out on the ground. This skill can only be developed with experience.
You will want to look over the Forest Service Trails Management Handbook (FSH 2309.18), Parker's "Natural Surface Trails by Design" (2004), IMBA's "Trail Solutions" (2004), and MTDC's "Building Mountain Bike Trails: Sustainable Singletrack" DVD (Davies and Outka-Perkins 2006). These references have a lot of good information to help you do a good job of trail layout.
Tools to scout the route include: clinometer, compass, altimeter, GPS receiver, flagging of different colors, wire pin flags, roll-up pocket surveyor's pole, permanent marker to write notes on the flagging, field book, probe to check soil depth to bedrock, and maps. The objectives of scouting or reconnaissance are to:
- Verify control points and identify additional control points
that you did not spot when you were studying the maps and
- Verify that the mapped route is feasible.
- Find the best alignment that fits all objectives.
- Identify additional positive control points to enhance the
- Validate that the route is reasonable to construct and maintain.
Hints for Locators
- Don't trust an eyeball guess for grade; use
your clinometer (clino).
- Large trees often have natural benches on their uphill side. It's better to locate your trail there than on the downhill side where
you'll sever root systems and generally
undermine the tree. Your specifications will
tell you how close the trail can be to the tree.
- Look for natural platforms for climbing
turns or switchbacks. They save construction
costs and better fit the trail to the land.
- Cross ravines at an angle rather than going
straight up and down the ravine banks.
- Flag locations for grade reversals.
- Look for indications of shallow bedrock,
such as patches of sparse vegetation.
- Flag the centerline location, particularly in
- Look for small draws to locate grade reversals.
The trail should climb gently for a few
feet on each side of the draw.
- Avoid laying a trail out on flat terrain because water has no place to drain.
Field scouting requires sound knowledge of map and compass and of finding your way on the ground. Begin with the theoretical route, then try different routes until you find the best continuous route between control points. Walk, walk, walk. Keep field notes of potential routes.
It may be useful to hang reference flags at potential control points or features so they are easier to relocate later.
Reconnaissance is easiest with two people. You and your partner need to use a clinometer to determine sustainable grades.
Building sustainable trail grades helps keep maintenance at bay. So what makes a grade sustainable? This design element comes from IMBA's "Trail Solutions" book (2004). It's called the half rule.
The half rule says that the trail grade should be no more than half the sideslope grade (figure 3). This rule really helps when putting trails on gentle sideslopes. For example, if you're working on a hill with a 6-percent sideslope, your trail grade should be no more than 3 percent. If the trail is any steeper, it will be a fall-line trail.
Fall-line trails let water funnel down, causing erosion and ruts. As sideslopes get steeper, trails designed using the half rule can be too steep. Use your judgment and knowledge of the particular area.
Specifications are important too. You'll want to refer to the Forest Service Trails Management Handbook (FSH 2309.18) for guidelines on building almost any type of trail.
All trails are not created equal. Ideally, each trail is designed, constructed, and maintained to meet certain specifications. These specifications are based on the recreational activities the trail is intended to provide, the amount of use, and the physical characteristics of the land. Ecological and esthetic considerations are also important.
For example, a narrow winding trail might be the right choice for foot traffic in the backcountry (figure 4), while a wider trail tread with broad sweeping turns would be appropriate for an ATV (all-terrain vehicle) route. A smooth trail with gentle grades (figure 5) is more appropriate for an interpretive trail or a trail designed for persons with disabilities. Challenging trails that include rocky boulder fields and some jumps might be designed for mountain bikes and motorcycles.
The steepness of the hillside determines how difficult a trail is to build. The steeper the hillside, the more excavation will be needed to cut in a stable backslope. Trail grade also has a direct bearing on how much design, construction, and maintenance work will be needed to establish solid tread and keep it solid. Grades range from 1 percent for wheelchair access to 50 percent or greater for scramble routes. Most high-use trails should be constructed with an average trail grade in the 5- to 10-percent range. Trails of greater difficulty can be built at grades approaching 15 percent if solid rock is available. Trails steeper than 20 percent become difficult to maintain in the original location without resorting to steps or hardened surfaces.
Use flagging tape to mark the trail opening or corridor. Use colors that stand out from the vegetation. Fluorescent pink should work in most areas.
You will need to use the clino to keep the trail's grade within the limits of the half rule.
Two or More Persons Flagging—Stand on the centerline point, direct your partner ahead to the desired location, then take a reading with your clino. When the desired location is determined, the front person ties a piece of flagging on vegetation with the knot facing the intended trail, then moves ahead. The person with the clino moves up to the flagging and directs the next shot. A third person can be scouting ahead for obstacles or good locations.
Using the Clino: Zeroing Out
- You and your partner stand on flat ground facing each other.
- Look through the clino and line up the horizontal line on zero.
- Open your other eye and see where the horizontal line intersects a spot on your partner.
- Use this spot on your partner for reading grades with the clino.
- Always read the scale on the right—this is the percent scale.
One-Person Flagging—Stand at a point that is to be the centerline and tie flagging at eye level. Then move about 3 to 6 meters (10 to 20 feet) to the next centerline point and sight back to the last flag. When you have the desired location, tie another piece of flagging at eye level.
Flagging the Route—Flagging marks your intended trail layout on the ground. While flagging the route, you will discover impassable terrain, additional control points, and obstacles that weren't evident on the map. Use different colors of flagging for the other possible routes as you lay in the trail options. Always use a clino to measure sustainable grades.
If you're working in heavy brush and you can't see your partner through the clino, have your partner wiggle a bright flashlight.
Start by tying flagging to the branches of trees at eye level and about every 3 meters (10 feet). Don't forget to tie the knot so that it faces the intended trail location. This way, if another crew continues the work, they will know your intentions.
Don't scrimp. Flagging is cheap compared with the time spent locating the route. Animals carry off flagging, and wind blows it down. Flagging that is close together helps trail designers and builders visualize the flow of the trail.
If you are working in an open area without trees or shrubs, use pin flags instead of flagging.
Marking the Final Alignment—Pin flags mark the exact location of the trail tread (figure 6). Pin flags can be placed on the trail's centerline or on its uphill or downhill side. Just make sure the crew knows where the trail will be relative to the pin flags. Place pin flags every 3 meters (10 feet) or so. More is better.
Now, run or walk the trail. This gives you a good feel for the flow of the trail. Make adjustments and move the flags if a turn feels too sharp or a section has too much straightaway. When your trail alignment feels really good and you're satisfied with the locations of the pin flags, have the land manager check your design. You'll need to have the manager's approval before cutting any vegetation or removing any dirt.
- Always use a clino to measure grades.
- Tie the knot of the flagging so it faces the intended trail.
- Line your intended trail with pin flags. Use plenty of these flags—they will help you visualize the trail flow.
- Run or walk this route. Make final adjustments to get the trail's flow just right before cutting any vegetation.
No discussion of trails is complete without attention to esthetics. We're talking scenic beauty here. Pleasing to the eye.
The task is simple. An esthetically functional trail is one that fits the setting. It lies lightly on the land and often looks like it just "happened."
Well-designed trails take advantage of natural drainage features, reducing maintenance that might be needed, while meeting the needs of the users. The trail might pitch around trees and rocks, follow natural benches, and otherwise take advantage of natural land features (figure 7).
The best trails show little evidence of the work that goes into them. A little extra effort spent limbing properly, scattering cut vegetation widely, blending backslopes, avoiding drill hole scars, raking leaves back over the scattered dirt, and restoring borrow sites pays off in a more natural-looking trail. Be a master. Do artful trail work.