IMBA Trail Difficulty Rating System

These ratings consider only the technical challenge of the trail, not it's length nor the amount of climbing!

 

Easiest
White Circle
 

Easy
Green Circle
 

More Difficult
Blue Square
 

Very Difficult
Black Diamond
 

Extremely Difficult
Dbl. Black Diamond
 

Trail Width

72" or more

36" or more

24" or more

12" or more

6" or more

Tread Surface

Hardened or surfaced (paved)

Firm and stable

Mostly stable with some variability

Widely variable

Widely variable and unpredictable

Average Trail Grade

Less than 5%

5% or less

10% or less

15% or less

20% or less

Maximum Trail Grade

Max 10%

Max 15%

Max 15% or greater

Max 15% or greater

Max 15% or greater

Natural Obstacles and Technical Trail Features (TTF)

None

Unavoidable obstacles 2" tall or less

Avoidable obstacles may be present

Unavoidable bridges 36" or wider

Unavoidable obstacles 8" tall or less

Avoidable obstacles may be present

Unavoidable bridges 24" or wider

TFF's 2' high or less, width of deck is greater than 1/2 the height

Unavoidable obstacles 15" tall or less

Avoidable obstacles may be present

May include loose rocks

Unavoidable bridges 24" or wider

TFF's 4' high or less, width of deck is less than 1/2 the height

Short sections may exceed criteria

Unavoidable obstacles 15" tall or less

Avoidable obstacles may be present

May include loose rocks

Unavoidable bridges 24" or narrower

TFF's 4' high or less, width of deck is unpredictable

Many sections may exceed criteria

 The IMBA Trail Difficulty Rating System is a basic method used to categorize the relative technical difficulty of recreation trails. The IMBA Trail Difficulty Rating System can:

This system was adapted from the International Trail Marking System used at ski areas throughout the world. Many trail networks use this type of system, most notably resort-based mountain biking trail networks. The system best applies to mountain bikers, but is also applicable to other visitors such as hikers and equestrians. These criteria should be combined with personal judgment and trail-user input to reach the final rating.

Trail Rating Guidelines

1. Rate Technical Challenge Only.

The system focuses on rating the technical challenge of trails, not the physical exertion. It is not practical to rate both types of difficulty with one system. Consider, for example, a smooth, wide trail that is 20 miles long. The technical challenge of this trail is easy, yet the distance would make the physical exertion difficult. The solution is to independently rate technical challenge, and indicate physical exertion by posting trail length, and possibly even elevation change.

2. Collect Trail Measurements.

Use the accompanying table and collect trail measurements for each criteria. There is no prescribed method for tallying a "score" for each trail. Evaluate the trail against the table and combine with judgment to reach the final rating. It is unlikely that any particular trail will measure at the same difficulty level for every criteria. Fore example, a certain trail may rate as a green circle in three criteria, but a blue square in two different criteria.

3. Include Difficulty and Trail Length on Signs and Maps.

Trail length is not a criterion of the system. instead, trail length should be posted on signs in addition to the difficulty symbol. A sign displaying both length and difficulty provides lot of information, yet it is simple to create and easy to understand.
           Likewise, elevation change is not a criterion. The amount of climbing on a trail is more an indicator of physical exertion than technical difficulty. Mountainous regions may consider including the amount of climbing on trail signs.

4. Evaluate Difficulty Relative to Local Trails.

Trails should be rated relative to other trails in the region. Don't evaluate each trail in isolation. Consider all the trails in a region and how they compare to one another. This will help you rank the relative difficulty of each trail and will help trail users select an appropriate route. Trails will rate differently from region to region. A black diamond trail in one region may rate as a blue square in another region, but the ratings should be consistent locally.

5. Use Good Judgment.

Rating a trail is not 100 percent objective. It's best to combine tangible data with subjective judgment to reach the final rating. For example, a trail may have a wide range of tread surfaces - most of the trail is easy, but some sections are more difficult. How would you rate it? Us your personal experience to consider all elements and select a rating that best matches the style of your trail.

6. Consider Other Trail Qualities.

Don't forget to consider trail qualities beyond the objective criteria. A wide variety of features could contribute to a trail's difficulty. For example, exposure - the feeling of empty space next to and below the trail tread - provides an added psychological challenge beyond the steepness or roughness of the trail. A 3-inch rock seems like a boulder when a 50-foot drop looms on your side! Other qualities to think about are corridor clearance and turn radius.

7. Use Common Sense and Seek Input.

No rating system can be totally objective or valid for every situation. This system is a tool to be combined with a discerning eye, and seek input from trail users before selecting the rating.
           Remember, a diverse trail network with a variety of trail styles is a great way to ensure happy visitors. Provide both easy and difficult trail to spread visitors and meet a range of needs. By indicating the length and difficulty of trails with a clear signage system, visitors will be able to locate their preferred type of trail easily.

Criteria to Consider

Tread Width: The average width of the active tread or beaten path of the trail.

Tread Surface: The material and stability of the tread surface is a determining factor in the difficulty of travel on the trail. Some descriptive terms include: hardened (paved and surfaced), firm, stable, variable, widely variable, loose and unpredictable.

Trail Grade (Maximum and Average): Maximum grade is defined as the steepest section of the trail that is more than approximately 10 feet in length and is measured in percent with a clinometer. Average grade is the steepness of the trail over its entire length. Average grade can be calculated by taking the total elevation gain of the trail, dividing by the total distance, multiplied by 100 to equal a percent grade. [Webmaster's note: the 'percent grade' is a measure of the rise of a trail divide by the horizontal distance it travels, also known as the 'rise over run.' To calculate the percent grade, divide the vertical distance by the horizontal distance traveled. For example, a 10% grade rises (or falls) 10' for every 100' horizontally moved. The actual length of the trail will be a little more than 100', 100.5' to be more exact. The slope of a 10% grade is 5.7 degrees. The astute browser will recognize that the percent grade is the same as the tangent of the slope, and a grade of 100% is the same as a 45 degree slope.]

Natural Obstacles and Technical Features: Objects that add challenge by impeding travel. Examples include: rocks, roots, logs, holes, ledges, drop-offs, etc. The height of each obstacle is measured from the tread surface to the top of the obstacle. If the obstacle is uneven in height, measure to the point over which it is most easily ridden. Technical Trail Features (TTFs) are objects that have been introduced to the trail to add technical challenge. Examples include: rocks, logs, elevated bridges, teeter-totters, jumps, drop-offs, etc. Both the height and the width of the technical feature are measured.


The above was taken from the IMBA periodical Trail News, Autumn 2004.

 

Thanks for looking at Steve's guide to mountain biking trails in Ventura County, the Santa Monica Mountains National Recreation Area (SMMNRA) and other locations frequented by the North Ranch Mountain Bikers.