Trails on Slopes

This trail leads straight over the hill.

A common mistake in establishing trails is to make them on slopes that are too steep for comfort and the environment. Such steep trails generally result in serious erosion, a wide swath of impacted area as walkers go to the sides to find better footing, and the inability of many hikers to walk the trail. An absolute limit for trail grades is a grade of one in six, and a more practical limit is a slope of one in eight. Trails that ascend steep slopes may use switchbacks (also called hairpins), but switchback design and construction is a specialized topic that takes great care. The best trail designs eliminate switchbacks.

If a trail is being made to be accessible to off-road wheelchairs, the grade should be no more than one in ten. If a paved trail has to be accessible to all wheelchairs, the grade must be no more than one in twelve, with periodic level pull-offs.

The off-slope, or side-slope, of the trail also must be considered. This is the slope of the trail from side to side, and should never be more than one in twelve. Side-sloped trails are prone to gullying. Ideally, the treadway of the trail should be almost, but not quite, level in cross-section.

Achieving the proper slope in hilly terrain usually requires the excavation of sidehill trail. This is trailway that is constructed by establishing a line of suitable slope across a hillside, then digging out by means of a mattock or similar tool to create the trail. This may be a full-bench trail, where the treadway is only on the firm ground surface after the overlying soil is removed and thrown to the side as waste, or a half-bench trail, where soil is removed and packed to the side so that the treadway is half on firm old ground and half on new packed fill. In problem areas, it may be necessary to establish the trail entirely on fill. In cases where filling is used, it’s necessary to pack it firmly and to revisit the site periodically to add to the fill and repack it until fully stable.