Trail Care Crew
Mtn Bike Patrol
Save the Trails!
Jan and Mike Riter, Subaru/IMBA Trail Care Crew
Download a blueprint for the switchback - switchback.pdf - a high resolution file suitable for printing (104k)
"Build it right. Ride it forever."
Have you encountered one of those really difficult to ride switchbacks that seem to get worse every time you ride? Do they quickly become a maintenance nightmare? Fortunately there is a solution!
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."
We recommend a design called the rolling crown switchback. Its principle goal is to allow trail users to execute the turn on a flat turning platform. The other key element is drainage control. The uphill leg leading into the platform is in-sloped, which is opposite of the general rule to out-slope trail treads. On the lower leg, the tread returns to normal out-slope. The joining of the insloped upper leg and the outsloped lower leg at the turning platform give it a slightly crowned shape which rolls away in all directions. The crown provides natural water shedding capability.
A switchback can often be the second largest construction project on a trail. (The largest is usually a bridge, a topic for another time.) It requires a small degree of engineering, proper placement, rocks, logs or other large building products, and a whole lot of sweat equitywhich is why you don't see them very often. However you should not be intimidated. Once these things are properly built, they tend to last for a long time, with little maintenance. Building the rolling crown switchback is a job for about 10 people any more than that and you'll just get in each other's way.
Chose the best spot to put the switchback. This would be the flattest area you can find that is still convenient for the trail. If the hillside is seven percent or less, you should put in a climbing turn. Anything over that, and a switchback must be built for longevity and protection of the environment.
The upper leg of the trail coming into the turn will be in-sloped for 30 to 50 feet above the platform so that water will drain off the backside of the turn. Make sure that you don't dig a trench here; it should just be gently in-sloped and extend past the turn so that the water will drain off the back side of your switchback in a wide, slow fashion, and never flow through the turn. The in-slope should be three to five degrees, and remember to cut the back-slope to the usual specification. The upper leg will also need to be dug down and into the back-slope, making the trail steeper before it enters the platform. This reduces the amount of fill necessary for the platform, shortens the height of the crib wall on the downhill side, and reduces trail users' temptation to shortcut the switchback.
The table itself has a minimum eight-foot diameter. A good way to measure this is to stand at the center of the turn and hold a shovel at arms length. The edge of the shovel should just reach to the outer edge of the turning platform.
The lower leg should come straight off the table in the form of a 30- to 50-foot long ramp to tie the table back to the downhill side of the trail. All of the lower part should be out-sloped for proper drainage.
Clear as mud so far? Good! Now, onto the construction process. First, give everyone on the project a good overview of everything that you are hoping to accomplish. Then start digging about 50 feet from where the center of the turn will be. Keep the excavated soil; you will use it later. Be careful not to dig too big of a ditch on the inner side of the tread, as it may give water a chance to start eroding your structure, as well as guide unwary users off the back side of the switchback.
While one crew is digging the uphill, in-sloped tread, others can start working on the crib wall that will form the outer edge of the table. Building all components of the structure together ensures that the lower half will be firmly tied into the upper half, not built as a separate unit.
Note that since the table will be flat and partially dug into the hillside, the crib wall will only have to be built about a half way around (good news for the crib wall crew). If green logs are used they should be stripped of their bark and pinned with rebar. Do not use old or dead wood, because it will rot and have to be replaced. Railroad ties, treated lumber and power poles also work well. If rock is used make sure it is stacked so that the wall leans into the table. Use the biggest, flattest rocks you can find. This will keep the mass of dirt behind it from pushing out. Once the crib wall is finished, take a break (you can call it "supervising" if that makes you feel better). After each layer of the crib wall is built, add a layer of soil behind it and pack it in as you go. Place the dirt in thin layers of two to three inches and pack it firmly with a McLeod or some other packing device. This will allow the structure to be used immediately after completion and prevent settling where the loose soil was placed.
After all is in place, kick everyone off the switchback and make sure everything is compacted, smooth, and properly in-sloped or out-sloped. Now get on your bike, put on your helmet, and ride it. The turn should be easy to execute in both directions, eliminating skidding or other impacts from users trying to negotiate an otherwise unridable turn.
When you return for future maintenance, you should only need to clean out the upper leg's drainage.