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Troy Hartwig's Diary

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My personal attempt to harmonize trail (Hiking and MTB) difficulty rating scales

Posted by Troy Hartwig on 8 August 2022 in English.
Class - Color - Title Description surface smoothness sac_scale trail_visibility Incline (peak rise/run) MTB : YDS : NFS : AWTGS : IMBA  
Class 0 - Grey - Accessible “Experience, Gear, and Risk: No hiking experience required. Suitable for wheelchair users who have someone to assist them. No risk.” “Asphalt, Chipseal, Fine Gravel, Paved, Concrete, paving_stones, Compacted, metal, wood” “Excellent, Good, Intermediate” N/A Excellent < 8% MTB 0 : YDS NA : NFS C5 : AWTGS G1 : IMBA 0  
  Surface and Visibility: Hardened or surfaced and clear.              
  Obstacles: Flat even surface with no steps or steep sections. No obstacles present (<1”).              
  Hands: Hands not required.              
Class 1 - Green - Easy “Experience, Gear, and Risk: Hiking on a well groomed trail. Athletic shoes sufficient. Map not needed. No Risk.” “Sett, unhewn_cobblestone, cobblestone, stepping_stones, unpaved, gravel, pebblestone, grass, grass_paver, sand, woodchips (potentially unpaved, rock, ground, dirt, earth, mud)” bad hiking (T1) Excellent < 40% MTB 1 : YDS Class 1 : NFS Class 4 & 3 : AWTGS G2 :IMBA 1  
  Surface and Visibility: Surface hardened or compacted. Vegetation cleared outside trailway.              
  Obstacles: May have a gentle hill section or sections and occasional steps or small obstacles such as roots and stones (<2”)              
  Hands: Hands not required.              
Class 2 - Blue - Moderate “Experience, Gear, and Risk: Hiking on a trail. Hiking boots recommended. Limited potential for falling.” “unpaved, rock, ground, dirt, earth, mud,” “very_bad, horrible,” mountain_hiking (T2) good <70% MTB 2 : YDS Class 1: NFS Class 2 : AWTGS G3 : IMBA 2  
  Surface and Visibility: Continuous established footpath. Vegetation may encroach trail. Partially steep terrain.              
  Obstacles: Obstacles common (<8”). Steps and flat stairs. Short steep hill sections.              
  Hands: Hands not required.              
Class 3 - Red - Difficult “Experience, Gear, and Risk: Simple scrambling. Average orientation/navigation skills. Sturdy hiking boots recommended. Some potential for falling encountered.” Same as Class 2 very_horrible demanding_mountain_hiking (T3) intermediate <100% MTB 3 & 4 : YDS Class 2: NFS Class 1 : AWTGS G4 : IMBA 3  
  “Surface and Visibility: Usually marked, but trail not always visible, and signage not always visible.”              
  “Obstacles: Obstacles common including large boulders, logs, and large steps (<15”). exposed passages can be protected with cables, Steep grades”              
  Hands: Hands required to maintain balance.              
Class 4 - Black - Very Difficult “Experience & Gear: Specialized hiking skills and gear, including navigation and emergency first aid. Weather exposed portions, rock ledges, fields, and slopes. Potential danger is encountered and fall protection may be recommended.” Same as Class 2 impassable alpine_hiking (T4) bad >100% MTB 5 : YDS Class 2: NFS Class 1 : AWTGS G5 : IMBA 4  
  Surface and Visibility: Tracks are likely to be very rough and unmarked.              
  “Obstacles: Characterized by blocky terrain with counter climbs, scree fields and landslides, high steps and fallen trees and extremely steep grades.”              
  Hands: Hands required to advance.              
Class 5 - Orange - Expert “Experience, Gear, and Risk: Scrambling with increased exposure. A rope could be carried. Good terrain assessment and orientation skills required. Falls could be fatal.” rock impassible demanding_alpine_hiking (T5) Horrible » 100% MTB 6 : YDS Class 3 : NFS N/A : AWTGS N/A : IMBA N/A  
  Surface and Visibility: Occasionally pathless.              
  Obstacles: Basic/easy climbing sections.              
  Hands: Handholds necessary to bear weight.              
Class 6 - White - Climbing “Experience, Gear, and Risk: Basic to advanced climbing.” rock impassible difficult_alpine_hiking (T6)     MTB 6 : YDS Class 4-5 : NFS N/A : IMBA N/A  
  Surface and Visibility:              
  Obstacles:              
  Hands:              

The Harmony of Difficulty Rating Systems

Posted by Troy Hartwig on 8 August 2022 in English.

When preparing to embark on a hike, I want to know if a trail suitable for me (my skill level and the time/energy I have for the hike). I would like to review a map and have trails clearly identified based on their level of difficulty and level of required exertion. There are numerous classification systems which grade trails for hiking and mountain biking including the Swiss Alpine Club Rating scale, German Single-track Scale, International Mountain Mike Association scale, Yosemite Decimal System, Australian Walking Track Grading System, the Sierra Club scale, the Appalachian Mountain Club, and Shenandoah National Park and Pigeon Forge National Park, and the US Forest Service and others. These rating systems variously take into account surface condition and obstacles, steepness, trail visibility, required gear, required wayfarer skills, risk/exposure, length, and elevation change.

Several of the established scales focus on exertion level based on length/elevation with different formulas but don’t take into account technical difficulty (National Park Service and Appalachian Mountain Club, Sierra Club). Several focus terrain and skill required with criteria for peak and/or average incline, surface material, smoothness, visibility, required gear, and risk/exposure (SAC, MTB, YDS, and USFS). While others combine these factors (Australian System, and Adventure Nerds). Others have proposed modifications/alternative scales that have not been widely adopted, but attempt to merge and isolate key factors.

OSM has well established tags for ways based on the Swiss Alpine Club Rating scale for hiking and the German Single-track Scale for mountain biking, but these are not always used. There are other tags that are related to the factors which contribute to the difficulty assessment (surface, smoothness, visibility, incline), again with variable adoption. The stamina and time required for a hike are a combination of elevation change and distance which are also OSM tags recommended for routes, but stamina and time will also be influenced by the technical difficulty of the ways.

Personally, I think it is useful to segregate the technical difficulty of a path from the exertion level required to complete it. I think it would be interesting to render a map with ways based only on technical difficulty, and routes based on a combination of difficulty and exertion required to complete.

I have taken a pass at correlating all of the various scales and harmonizing their criteria and factors, and then identifying the values for the relevant tags in OSM. The scales are not entirely consistent, so this table represents a number of choices I have made. I intend to use this table along with an algorithm to render trail difficulty based on a combination of whatever tags are available. Such an algorithm could also flag paths which are missing critical information about difficulty or have confusing/conflicting metadata potentially in need of validation (e.g. surface=paved & sac_scale=mountain_hiking, or smoothness=horrible & mtb:scale=0). I have also started on a MapCSS style for JOSM based on this table for my own use and exploration, I hope to upload it to github shortly. I also intend to expand the algorithm to take into account access indications as being identified by the trails working group.