Trail Design and Construction

Susanville Ranch Park trails feature a series of
 undulations but an average grade of only 4.5%

As published on AmericanTrails.org
By Randy Martin, Trailscape

Optimizing trail grade: the key to creating sought-after trails

Designers and land managers should consider the benefits of lengthening trails to lower the average grade while at the same time including short sections that are much steeper.

Designing trails that maximize the user’s delight while minimizing the drudgery may be the trail building community’s best way to help energize local economies. It may be a small contribution, but recovery is a process of people becoming confident and deciding to move forward, this could be our part.



Delight vs. Drudgery

Foresthill Divide and Connector, Auburn CA

Too often, trails are designed in a manner that causes the user to experience unnecessary drudgery with too little delight, thus discouraging repeated use of the trail. Tourists do not travel to Disneyland to ride the parking tram, they go for the Matterhorn. In many areas, tourism is the life-blood of the community, so if the goal is to increase tourism by creating trails, we must keep in mind that a person considering whether or not to travel and use a trail is forgoing a long list of other interesting options. As trail builders and designers we must seek to make our trails attractive.
The purpose of this article is to encourage designers and land managers to consider the benefits of lengthening trails to lower the Average Grade while at the same time encouraging the building of short sections with a Specific Grade (5-10 feet of vertical) to be as steep as the condition will allow. For the sake of simplicity, let’s call this Minimize/Maximize Design.

The key to an enjoyable average tread grade is to keep it as low as reasonable while fulfilling the objectives of the trail. It may be that an objective is to get to the summit, a pass, or to a vista. Most designers I have worked with tend to set the grade at 10% and grind it out. Minimize/Maximize Design lowers the average grade to 4-6% and doubles the length of the trail in a series of grade adjustments.

The optimal average grade will allow higher speed going uphill and releasing earned elevation slowly rewards the user with a nice, long downhill. It is discouraging to spend 40 minutes grinding up a hill only to use it all up in 2-3 minutes. As a friend of mine says, “You want to consume that ice cream cone one lick at a time.”

Although it takes some energy to place one foot in front of the other or roll on the flats, the key heart demand is based on how much elevation is being gained or lost. Depending upon what shape we are in will determine how many feet of elevation per minute can be accomplished. I like to think of elevation in terms of flights of stairs per minute. Let’s say a runner is in pretty good shape and can run eight miles per hour while gaining 10 feet of elevation each minute, (one flight of stairs). That same runner would slow to about 1-2 miles per hour if the sustained grade is 16% (eight flights of stairs per minute). The climbing rates for a bicyclist are similar. Who wants to ride a bike or run under 2 miles per hour? Not me!

The downhill direction is a different experience. The designed grade dictates if the experience is a delightful payoff for the work done to get to the top or just a leg pounding, brake burning, trail grinding experience. If the tread grade is 10% or more, a cyclist will often be on the brakes, which is not much fun and can be hard on the trail. The runner will be in small step braking mode, as are horses and hikers. At a 4% grade, the cyclist can pedal downhill or coast without much braking and a runner can flow effortless down the hill with minimum pounding. As a runner, it is pure delight to be able to run fast downhill without the associated pounding from braking with every step.

The average grade of of this trail is 4%, yet in a 700 foot ascent the grade varies from -5% to 20% and changes 10 times

The average grade of of this trail is 4%, yet in a
700 foot ascent the grade varies from -5% to 20%
and changes 10 times

Specific Grade

There is much discussion of maximum average grade in terms of its sustainability. Rarely have I seen discussion about specific grade. In other words, how steep can a trail tread be for 20 to 40 feet and still be resistant to erosion? Consideration for erosion include soil conditions, typical rainfall, characteristics of the rain delivery, tree canopy, wind, and level of trail use. To maximize the delight of the trail, the specific grade should vary as widely as reasonable. The table to the right is an example of a trail with an average grade of 4%, yet in a 700 foot ascent the grade varied from -5% to 20% and changed 10 times. This is one way to make a trail interesting..

What is called the half rule applies to specific grade: The slope of the trail should not be more than one half the cross slope. This has the most application in less steep areas. The reason for this rule is if the trail is too steep, relative to the slope of the hill, water will tend to collect and run down the trail instead of sheet flowing across the trail and down the hill. Keep in mind that every turn violates this rule at one point. Grade reversals (dips), if used generously, force the water off the trail and can counter violations of this rule.

Foresthill Divide and Connector, Auburn CA

In Auburn California we have a trail where the average grade from top to bottom over 7 miles is only 1.4% while the specific grade ranges from -20% to +22%. It is famous in the region. The lack of a need to summit freed this design to promote plenty of undulating fun in both directions.

Susanville Ranch Park Expansion

Last fall, Trailscape inc. contracted for the finish flagging and construction of 14 miles of trail in Susanville, California. The terrain dictated over 1000 feet of climbing and we were able to stretch the climb to just over 4 miles and we averaged 4.5% grade. As you see below, the climb is fairly steady but is made up of a series of undulations which create delight while climbing and a roller coaster on the way down.

Susanville Ranch Park

User groups Minimum/Maximum design does not serve well

Physically Challenged: if a 30’ undulation is up to 20% tread grade the accessibility of the trail is minimized. To serve this group while maintaining the excitement, I would keep the maximum tread grade down to 8% on short sections for the first mile from the parking area.

Robust Hikers: One of the challenges for a hiker is that they can only walk so fast before it becomes a run. Often retired, runners turn to hiking as they get older and they rely on a steep trail to get their heart rate up. The short sections of intensity may not satisfy them. To help serve this group, one leg of the loop could be a gradual climb to the summit and one leg of the loop could be made steeper for more advanced hikers.

Extreme Equestrian and Mountain Biking: For the more adventuresome Minimum/Maximum design will not generate the adrenaline desired by the more extreme enthusiasts but it will serve them better than a consistent grade. To help satisfy this group, more difficult optional trail segments may be built in to satisfy some this need.

Challenges

• While designing to minimize average grade, the legs of a switchback can be very close together if the trail is climbing up a limited corridor. This might promote cutting a trail from leg to leg. To counter this, it may be worth steepening the trail near the turns to gain an immediate separation. Another option would be using foliage or other means to visually block the view from trail to trail.
• Balancing efficiency with healthy undulation and meander: turning and undulating the trail should have some reason, for instance a tree or a boulder. Otherwise it may seem contrived and frustrating, especially to the hiker.
• A trail with a lower grade will have to be longer to get to a summit. The benefits of minimized trail grade must be balanced with available resources.

User groups this trail design serves:

•  Wide range of mountain bicyclists; not beginners or downhillers.
• Wide range of runners
• Wide range of equestrians; not extreme or beginner
• Low to mid range hikers; not the super fit.

In every group except hikers greater physical demand can be attained by going slightly faster.