Special Structures (continued)

A switchback consists of two approaches, a landing or turn platform, a drain for the upper approach and platform, and guide structures. The upper approach and the upper half of the turn platform are excavated from the slope. Part of the lower approach and the lower half of the turn are constructed on fill (Figure 60).

Figure 60—Switchbacks with a radial turning platform.

The approaches are the place where most of the trouble with switchback turns start. The approaches should be designed for the primary user group. In general, the last 20 m (65 ft) to the turn should be as steep as the desired challenge level will allow. This grade should be smoothly eased to match that of the turn in the last 2 to 3 m (6.5 to 10 ft).

Do not "flatten" the grade 20 m (65 ft) before the turn. If anything, steepen the approach grades to foster the sense that the switchback is the most convenient way of gaining or losing altitude. There is absolutely nothing as infuriating as walking a nearly flat grade to a distant switchback turn while looking several meters over the edge at the nearly flat grade headed the other direction. You can build a Maginot Line of barricades and still not prevent people, packstock, and wildlife from cutting your switchback. The only exception is a trail designed primarily for wheeled vehicles. The flatter approach makes control easier.

As the upper approach nears the turn, a grade dip should be installed. The tread below this point should be insloped until the halfway point in the turn. Both sides of this trench should be back-sloped to an angle appropriate for the local soil. As the turn is reached, the tread should be widened 0.5 m to 1 m (1.6 to 3.2 ft) wider than the approach tread. This is particularly important on small radius turns and for wheeled vehicles. It's less necessary for hikers and packstock.

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