Switchback Theory and Principles.


Abstract

Presenting the theory and principles of switchbacks, an essential element in sustainable trail design and construction, based on an exact definition of switchback and strict respect for grade.

Introduction.

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I used to say that I hated switchbacks. As a hiker I found them all too often too narrow, too steep, severely eroded, and generally just ugly. As a trail builder I was frustrated that I didn't know how to build them any better. But after many years of building trail – and perhaps more importantly, of observing and analyzing trail and trail problems – I finally figured out what the problems are, and what the principles are for building good switchbacks. These are what I present here – the theory and principles of switchbacks.

The perspective here is primarily that of a trail designer seeking to avoid failure of trail built in soil and on slopes. Aesthetic, 1 ecological, recreational, and political aspects of trails and trail building are not addressed.

Neophyte trail-builders should note that this is not a complete lesson in actually building switchbacks, as I am not (for the most part) going to cover techniques (unless they are new), tools, or various other aspects of building trail; these are covered quite well elsewhere. But the best tools and techniques are worthless if the fundamental concepts and plans of what you are doing are neither correct nor useful, and for fixing that everyone, neophyte and expert, should find this material useful.

Definition of 'switchback'.

Switchbacks are frequently bad because the people building and maintaining them do not really understand them. This is not news, as over the years absurd definitions and meaningless distinctions have led to a profound misapprehension of the concept – and a lot of seriously bad trail. To correct this requires review and revision of the fundamental concept and definition of 'switchback'. This is a prerequisite for what follows; please do not skip it.


Okay, that was a lot of material, but hopefully all qualms and concerns have been adequately addressed, and you now understand and embrace the new definition of "switchback". (No?? Then please review definition of 'switchback' again.)

Grade.

We have seen that switchbacks are mostly traverses with an occasional turn. For traverses generally and turns especially one of the most important factors bearing on whether tread will fail (and our efforts be wasted) or not is grade. Maintaining a proper grade is the most important engineering requirement in designing and building trail, so there is a lot of material to cover. The main principle is to respect grade, and particularly to not exceed the maximum grade at any point. While understanding that alone may be sufficient for understanding some of the subsequent material, if you want to actually build or maintain trail, or to consider real-world cases, you will need a good grasp of the material on grade.


Again a lot of material. But if you want to understand and effectively apply these principles, to build any kind of sustainable traverse, switchbacked or not, you need to have an intuitive grasp of the fundamental principles and techniques of grade.

Traverses.

Switchbacks are mostly traverses, with an occasional kink. Before proceeding we need to work out a few problems that arise with traverses.

Turns.

Now we will get into the fundamentals of those kinks. A key finding is that all simple turns can be characterized with just four parameters. Knowing those plus a few more can be used to generate a vast landscape of switchback turns.

Geometrical development of a switchback.

A single traverse on a slope is geometrically simple. Two of them intersecting gets complicated. This section uses three-dimensional views to illustrate the basic problem and some of the complications, and various ways of handling it. The key to understanding a switchback is to understand its geometry. Don't miss it!

Measuring grade.

The need to measure grade is a fundamental principle of this theory, and actual measurement is essential to its application. This is a practical section, describing tools and methods suitable for measuring grade.

Flagging and staking a turn.

What good is a theory if you can't apply it to real life? This section illustrates how to flag and stake a switchback turn for construction.

Tips and odd bits.

Not really part of the theory, but we would not want your switchbacks to fail for having overlooked something simple. So here are some useful tips and odd bits.


Epilogue

I have come to like switchbacks, and especially the tricky parts, the turns. They can certainly be challenging, but there is no need to hate them, and certainly no need for them to be ugly. Just take the time and effort to give them the care and respect they deserve.

This theory is not yet perfect (just as these pages are not yet perfect), but I hope it will resolve some long-standing issues – and eventually lead to better trail. Suggestions for improvement can be sent to me at jj@scn.org.


Notes.

  1. Troy Scott Parker has made an excellent start on the aesthetics of trail. See his book Natural Surface Trails by Design: Physical and Human Design Essentials of Sustainable, Enjoyable Trails.

Copyright (C) 2008 by J. Johnson.


My thanks to the wonderful folks at the Wallingford Tully's for a super work environment.


These pages come to you from Seattle Community Network.