Switchback Theory and Principles:

Various definitions of 'switchback'.

Definitions of 'switchback' abound, but are universally unsatisfying. Following are various definitions dredged up from the Internet at the end of May 2008, showing how matters were at that time.

Some dictionary definitions:

en.wikipedia.org/wiki/Switchback :

  a road or trail joined by hairpin bends.
Switchbacks [Inclines1.png 3 KB]

Gravity Incline with Switchbacks

www.askoxford.com/concise_oed/switchback :

  noun 1 Brit. a road, railway, etc. with alternate sharp ascents 
  and descents. 2 a roller coaster. 3 N. Amer. a hairpin bend.

"Sharp ascents and descents"? Does sound like a roller coaster, and not what we have in mind. But take a closer look: the original Mauch Chunk Switchback Railway, a gravity railway that lowered cars through a series of alternating inclines, or switchbacks, later became the prototype of the roller coaster. The British public, not familiar with its original meaning, apparently then confounded "switchback" with this other aspect of the amusement rides.

www.merriam-webster.com/dictionary/switchback :

  a zigzag road, trail, or section of railroad tracks for climbing a steep

www.answers.com :

    1. A road, trail, or railroad track that follows a zigzag course on a
    steep incline.
    2. A sharp bend in a road or trail on a steep incline.

    To proceed in sharp turns in alternating directions on a steep incline.

Aside from reminding us about 'zig-zags', those were quite unhelpful. So let's check with one of the principal and most experienced sources of trail building information, the United States Forest Service. Their Standard Specifications for Construction and Maintenance of Trails defines a "switchback" as:

  Switchback. A reverse in direction of a trail grade with a level landing
  used to change elevation on a steep slope, usually involving special
  treatment of the approaches, barriers, and drainages.

Somewhat better, but still inadequate. Landings are not mentioned in a 1990 USFS Guide for Mountain Trail Development, and as will be explained later, a "level landing" is not required for a switchback except in one special case, which in actual practice rarely occurs. An important point, as the Forest Service's Trail Construction and Maintenance Notebook (1996 edition, p. 84; see www.fhwa.dot.gov/environment/fspubs/00232839/page10.htm at the Federal Highway Administration site) relies on the presence or absence of a landing to distinguish between switchbacks and climbing turns:

  Switchbacks and climbing turns are used to reverse the direction of travel
  on hillsides and to gain elevation in a limited distance. What is the
  difference between the two? A climbing turn is a reversal in direction
  that maintains the existing grade going through the turn without a
  constructed landing. A switchback is also a reversal in direction, but has
  a relatively level constructed landing (Figure 57). Switchbacks usually
  involve special treatment of the approaches, barriers, and drainages. They
  are used on steeper terrain, usually steeper than 15 to 20 percent.

(See also the 2007 edition at www.fhwa.dot.gov/environment/fspubs/07232806/page12.htm which is nearly the same, adding: Switchback turns have pretty tight corners because of the steeper grades – which is quite incorrect, as grade has nothing to do with the radius of the turn. There is some excellent information here, but I find some parts to be dubious. Evaluate cautiously.)

Many trail builders were taught this definition, and find it acceptable; it does seem to offer a clear resolution of this long simmering supposed issue of the difference between switchbacks and climbing turns. My thesis is that it is not adequate, and even incorrect, which I will be explaining in detail, but for now let's see if anything better can be found.

From various sites (italicization added):

www.scottsdaleaz.gov/Assets/documents/design/dspm/2006/Definitions.pdf :

  A sharp short radius curve in a trail that is used on hillsides to reverse
  the direction of travel and to gain elevation. Switchbacks have 
  relatively level turning platforms.

Relatively level?

http://www.railstotrails.org/ourWork/trailBasics/glossary.html :

  Switchback: A sharp turn in a trail (usually constructed on a slope of
  more than 15%) to reverse the direction of travel and to gain elevation.
  The landing is the turning portion of the switchback. The approaches are
  the trail sections upgrade and downgrade from the landing. 

www.imba.com/news/trail_news/12_4/itn_12_4.pdf and
www.imba.com/resources/trail_building/switchbacks.html :

  Most of us think of a switchback as a sharp 180-degree turn that follows
  the existing grade of the side slope or hillside. But that is actually the
  definition of a climbing turn, not a switchback. A more appropriate
  definition for a switchback is: "a structure that the trail leads into,
  makes a flat turn, then leaves in another direction."

Whoa! The previous definition said switchbacks are "sharp turns", but here "that is actually the definition of a climbing turn".

www.wta.org and www.tahoerimtrail.org :

  Switchback - A sharp reversal in the direction of the trail, allowing the
  tread to maintain a reasonable grade as it climbs a steep hillside.

WTA (article in SignPost magazine, 2004, old.wta.org/~wta/magazine/1097.pdf , scroll down to "Climbing Turns and Switchbacks"):

  In a switchback, the uphill portion of the turn is in-sloped....
  a climbing turn is normally more gradual than the switchback,
  and the upper portion of the turn is usually out-sloped....
  The notable feature of a clmbing turn is that it does not have a
  a typical landing in the turn, but has a more gradual trail turn.

Not having a typical landing is a notable feature?

www.trailville.com/wiki/Info:Trail_Glossary :

    a section of trail with dramatic sharp changes in direction (greater
    than 90 degrees). Switchbacks are often used on slopes to allow the
    trail to take a more gradual grade by zigzagging back and forth across
    the fall line as it climbs or descends the hill. Switchbacks are also
    common on mountain bike trails to provide interest and produce more
    miles of trails in a small area.

A "sharp turn", "sharp 180-degree turn", "sharp" and even "dramatic sharp changes in direction" – there certainly is a shared theme here, but "sharp" needs definition, and "180-degree turn" surely can't mean that exactly. But the "zigzagging back and forth across the fall line" is promising.

While it is true that running switchbacks across a slope instead of going straight up will "produce more miles [?] of trail", that is not the reason for building switchbacks.

"Best practices" in Ontario at www.abilitiescentre.org/trails/appendixa.html :

  A trail alignment crossing back and forth (zigzagging) across a steep
  slope to make it easier for the user to traverse up or down the slope.

www.hike-nh.com/faq/glossary :

  A trail that travels diagonally and turns back on itself in order to allow
  progression up a steep section of a mountain.

From the Appalachians ( www.whiteblaze.net ):

  A turn that takes the hiker 180 degrees in the opposite direction. 

From California State Parks and Recreation via Foresthill Trails Alliance ( www.foothill.net/fta/work/trailmaint.html):

  A "switchback" is any place where the alignment of a trail traverses a
  slope in one direction and then abruptly "switches back" toward the
  opposite direction

This definition comes very close to truth, but the "abruptly" is troubling.

www.joinomba.org/cora/ (Cincinatti Off Road Alliance):

  Switchback - A sustainable turn on a hillside. The trail is routed onto a
  level deck where it makes a transition to the opposite direction.

The "sustainable" part intrigues me, but unfortunately it is not explained, and the rest of the definition is inadequate.

www.americantrails.org/resources/info/TrailTermCOTI.html :

  Switchback: A sustainable turn on a hillside which doubles back or
  "switches back" on itself. The trail is routed onto a level landing or
  deck where it makes a transition to the opposite direction. The lower leg
  of a switchback is outsloped but the upper leg is insloped to drain water
  run-off out the end of the turn. Switchbacks were originally designed to
  allow railroads to carry traffic up steep, difficult terrain. They were
  called switchbacks because the rails included a switch to allow the trains
  to "switch back" on themselves.

From Breckenridge, CO ( www.townofbreckenridge.com/documents ):

  Climbing turns and switchbacks are curves in the trail that reverse the
  direction of travel. They may be needed to reduce grade when gaining
  elevation.  Climbing turns are wide, ascending curves that work only on
  gentle to medium slopes of less than 20%.  They are preferred over
  switchbacks because they are easier to construct and use. A switchback is
  a sharp, short radius curve that should be used as a last resort on
  hillsides where the working area is limited and slopes are greater than
  20%.  Switchbacks are difficult to construct, require continual
  maintenance, do not always accommodate mountain bikes, and are a challenge
  to manage because users may shortcut the turn.

www.bcmbg.com/resources/trail_building/trail_building_basics/Chapter4.htm (British Columbia Mountain Bike Guide):

  A switchback is a structure that makes a level turn throughout the
  transition, and then is routed in a new direction.

  Key features:

  o        Drainage runs off the back of the turn

  o        Flat table (the turn) forces the trail to cross the fall line of
  the hill. Users are turning on a level platform. The trail stays on the
  contour in both directions.

  o        Split the difference between cutting down and building a crib
  wall. Use material excavated from the top leg to build up the bottom leg
  behind the crib wall.

  3.      Most turns that are described as switchbacks are not actually
  switchbacks. They are climbing turns (Click here for a full climbing turn
  diagram). A climbing turn is a turn that climbs (or descends) the existing
  grade of the hill to make a steep, tight turn.

  4.      Climbing turns should be used on slopes less than 7% grade and
  have at least 75 feet between the upper leg and the lower leg (where the
  turn begins and ends).

The last three examples also show how definitions sometimes expand into characterizations and such, which may all be correct and even useful, but tend to confuse the definition.

USFS generic switchback (type 1) [fs-sb1-50.gif 6 KB]
USFS generic climbing turn [fs-ct-50.gif 4 KB]

Would a picture serve better? Compare the Forest Service's standard drawings for a generic "climbing turn" (right) and a generic "switchback – type I" (far right). (Extracted from the USFS 912_10 and 914_1 drawings.)

What is the difference? Both plan and cross-section views are nearly congruent. The main difference seems to be the presence of a drainage ditch in one (the very comment I heard from another trailbuilder regarding the WTA's definition) and a "barrier" (apparently of rock), but this could be simply because one drawing was done with more detail than the other. The only real difference here is that one plan says to maintain a constant grade, and the other specifies a maximum grade of 5%. Such a difference seems more accidental than significant, not even mentioned in the Forest Service's own definitions. For all practical purposes there is no difference here; these two configurations are effectively identical.

For all the importance that has been attached to distinguishing "switchbacks" from "climbing turns", none of the definitions that have been offered heretofore provides any basis for such a distinction. At best they offer only relative characterizations, such as one instance being "sharper" (etc.) than another. How do any of these definitions help us understand what a switchback is? Or help in building one?

Two Turns (1) (reduced size).  twoturns1x.gif 1 KB

If you think any of these definitions are useful, and that there is any real difference between "switchbacks" and "climbing turns", then consider: what kinds of turns are these in the diagram to the right? What are their defining characteristics? Come, if any of these definitions are useful, then use it: what kind of turns are these? What are the essential differences? We shall return to this later.

The conclusion I draw from all of these examples is that many people are struggling to define 'switchback', or even to distinguish it from something else called a 'climbing turn', but failing. Confusion abounds.

Enough. I can do better.

Back to Definition of 'switchback'.

Back to Switchback Theory and Principles.

Copyright (C) 2008 by J. Johnson.