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The Adaptable Terrain Classification System – Erik Kondo

Updated: Feb 5, 2023

Wheelchair user on an outlook point with mountains in the background.
Outlook point in Rangley Maine

The Adaptable Terrain Classification System (ATCS) is for rating various types of terrain. It provides wheelchair users, designers, and adaptive mobility product manufacturers a means to easily describe and compare different types of existing terrain encountered by wheelchair users. For example, it is not descriptive enough to say that a trail is either Wheelchair Accessible or Off-Road. The ATCS allows for more granular descriptions given the wide variety of terrain that exists in the environment. The ATCS follows the concept of the rating system of rivers for whitewater rafting and the Yosmite Decimal System (YDS) for rating the difficulty of walks, hikes, and climbs. The ratings are necessarily to facilitate communication, preparation, and suitability for different rivers, routes, or rock climbs. The underlying point is that human beings vary widely capability, skill, and experience. Therefore, it is critical for rafters, hiker, and climbers to know what they are getting into, and to bring along appropriate equipment and experience.

On the other hand, Accessible Trails are intended to be universally accessible to all disabilities. As a result, unlike trails for people without disabilities, no differentiation is made for individual capability, skill, and experience. While Accessible Trails are a very important aspect of nature preserves and parks, they are intentionally not challenging in order to facilitate access to nature by “the disabled”.

The "disabled” are seen as a monolithic group. Whereas, the “able-bodied” are seen as a wide variety of individuals with differing levels of wilderness skills, experience, and desire for personal challenge. The result is that a person with a disability has no way of gauging the suitability of a trail that is not designated as Accessible. The strict guidelines for Accessible trails create a situation where the vast majority of trails are not officially Accessible. But some of these trails may be adaptable. By describing existing trails with their ATCS rating, a new universe of possibilities arises for people with disabilities to challenge themselves and increase their wilderness skill and experience.

The following are my descriptions for rating terrain as Adaptable. As with YDS, this method is somewhat subjective to the person making the rating. The more people who rate particular area of terrain or trail, the more likely a consensus will form.

Adaptable Terrain Class 0

Official Wheelchair Accessible. Flat, hard, and spacious surfaces with ample turning room and no obstacles. The terrain is ideal for wheelchair use.

Also, relatively smooth and even surfaces. The terrain is easily navigated using a wheelchair or electric scooter. Examples are carpets, sidewalks with minor cracks and minimal uneven surfaces, wheelchair ramps, low thresholds, minor side slopes, curb cuts, brick sidewalks. Low wheel torque generation required.

Adaptable Terrain Class I

Slightly rougher, softer, and more uneven surfaces than Class 0. Minimal incline/decline. Terrain can be managed using a manual wheelchair with some effort. Most power wheelchairs should work fine. Examples are wide stone dust paths, packed gravel, packed dirt, minor bevels and side hills, well maintained dirt roads. Low wheelchair fall risk. Low wheel torque generation required.

Adaptable Terrain Class II

Uneven ground, rooted dirt paths, hard sand, dirt trails, small roots, leaves. Well maintained lawns. Very low curbs. Similar to Class I, but with minor inclines/declines, cross slopes, and a little rougher terrain. Most manual wheelchair users and power wheelchair users can navigate the terrain, although some may have difficulty. Minor wheelchair fall risk. Low/moderate wheel torque generation required.

Adaptable Terrain Class III

Somewhat tricky for wheelchair navigation. Much rougher, much softer, and much more uneven and narrow surfaces with some obstacles. Characteristics are large cracks, roots and rocks, curbs, loose gravel, shallow sand, narrow paths, wild grassy fields, dirt, rocky slabs, meadows, side slopes, wet and soft ground. Occasional high grass. Twists and turns. Steeper inclines/declines and cross slopes. Moderate fall risk. Moderate manual wheelchair skills and wheel torque generation required for navigation. Standard power wheelchairs are likely to be unable to navigate the terrain. Off-road adaptive devices should manage easily.

Adaptable Terrain Class IV

This terrain is very difficult for most wheelchair users. Adaptive equipment is typically required such as a trike-wheel and knobby tires, or off-road wheelchairs, handcycles, etc. It is characterized by very rough surfaces, large cracks, drop-offs, creek beds, steep inclines/declines and cross slopes, narrow twisting trails with obstacles, large roots, rocks, soft sand, obstructions, muddy, snowy, icy/snowy surfaces, shallow water. Able-bodied assistance may be required on occasion. High fall risk. High level wheelchair skills and wheel torque generation required for navigation. Off-road adaptive devices very helpful.

Adaptable Terrain Class V

This terrain is extremely difficult for wheelchair navigation. It typically requires the manual wheelchair user to obtain significant able-bodied assistance to get around. It is characterized by large rocks, snow, extreme side slopes, deep water, major obstructions, unstable surfaces, steps, very uneven terrain. Steps, stairways, and very steep hills in urban environments. High fall risk. Potentially high fall consequence. Very high level wheelchair skills/special techniques/adaptive mobility equipment/wheel torque generation required for navigation.

Adaptable Terrain Class VI

Completely unsuitable terrain for wheelchair use. It is likely that a wheelchair user will need to be physically carried for much of the way by able-bodied porters. Very specialized adaptive mobility devices required, but still may not be sufficient for navigation.


In order to further describe the terrain. Each Class can be further subdivided by the addition of a integer behind a decimal point. For example, Class III.1 is close to Class II.9 and Class III.5 is the the midpoint between Class III and Class IV.

The goal of the ATCS is to enable people with disabilities to challenge themselves in nature as they desire. And to allow them to take advantage of the huge amount of existing nature trails that are inherently not Accessible. In addition, the natural result of more people with disabilities in natural settings will be to encourage the development of more Accessible Trails.

Note that while the rating system is primary in reference to adaptive wheeled mobility devices, a person with some other type of mobility impairment, not requiring wheelchair use, such as visual or limb impairment should be able to interpret the ratings and apply them to their personal situation. How would you rate the terrain in the video below and why?

1 Comment

Jun 03, 2023

I'd rate the terrain in the video as III.5, maybe higher. Yeah, higher - IV.1 Narrow, twisting, uneven, cross slopes, asst may be required, mod-high wheelchair skills- perhaps only mod fall risk? As you say, it's somewhat subjective. I like the concept!

Dan Combs - 6 yrs T-10, 62 yrs old

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