Getting back on topic.
If I remember my conversation with the former trails manager of SEKI properly, Class 1-3 are allowed in designated wilderness areas and Class 4/5 are reserved for frontcountry trails. The new Soda Springs trail in Tuolumne Meadows is in violation of that general rule, but it’s so overused I assume they got some waiver for that due to overuse impacts. I don’t recall these ratings aren’t generally conveyed to the public - SEKI has an interactive web map that lists these details, but I don’t think they’re listed on park guides etc, which seems like a bit of waste as they could be described in terms of “experience/challenge” in a way that would be digestible.
That document does a great job of showing multiple examples of terrain and explaining things in detail, and I’d say that it’s more useful than the current solutions of trail_visibility and sac_scale. I do feel like we’ll need more than 1-2 photo examples of different levels no matter what system is decided upon, as there are just a lot of different ways that terrain within a value can exist. It’s probably a little verbose/long, but is a good case where having more text makes things clearer vs trying to fit everything into a short sentence.
That said, I am wary of combining visibility and obstacles / difficulty into a single rating - for formal trails it makes sense because an agency can control all aspects of a trail to create a certain experience (given sufficient funding).
There’s a significant amount of trails on OSM that aren’t formal. operator=none would clearly indicate that the system is being used for non managed trails, but then you can’t guarantee that something with the visibility of Class 3 won’t have occasional Class 1 obstacles.
Also having written up guides for a number of off-trail alpine passes that generally range from YDS 2-3 / SAC T2-4 terrain and answered questions on them, I can say there are a lot of people that are comfortable with obstacles that require use of hands for balance, but not simple climbing (even if it is unexposed). I don’t think it’s appropriate to get into 3+ levels of “climbing” on base difficulty but I think something like the following levels should exist (wording is placeholder), maybe not as highway types but as path:difficulty=* or something.
Four basic levels of difficulty that’d make sense to me if we go for an overall rating that then maps to regional ones (I had started on this idea in the link above). Very rough draft here, but it seems like these would cover major break points in terms of experience, comfort, and technique.
- 1 - path / simple-path NFS 4-5, SAC T1, YDS 1. some lower (there are plenty of low to moderate visibility trails over easy smooth terrain). anyone in moderately good health that is able should be able to traverse the terrain.
- 1.5 - uneven path NFS 3?, SAC T2, YDS 2 the above, with obstacles below knee height (some rocks in the trail, roots, etc) that can cause issues for people with mobility or balance issues. this could be a subset of the above, and that would make sense to me - these trails often exist alongside them and aren’t really marked any differently. if we want to get fancy, having a smoothness key that isn’t solely for vehicles would allow for the distinction between T1-T2 / rough YDS 1 while still keeping it to the same parent category.
- 2 - demading-path NFS 1-2, SAC T3, YDS 2. where hands have to be used for balance, maybe an occasional mantle or drop but no real “climbing” required. trails with ladders or other simple aids would fall into this category. requires more body strength and while trivial for most people, can be impassible to certain groups of people and inexperienced hikers may find it uncomfortable. many trails in Needles & Acada fall into this category for formal NPS stuff.
- 3 - scrambling NFS 1 / informal, SAC T4+, YDS 3. you have to use your hands to climb up / go over obstacles, but the terrain isn’t difficult/technical enough for the majority of people to want to be roped or use any aid gear. while the majority of people are probably capable of this, many unexperienced people will be uncomfortable doing it and some previous experience is highly recommended.
Anything above scrambling can be put into climbing. If we do go the highway route (which will have a lot of pushback) it’d be simple to then break down scrambling into more granular detail (ala SAC, British scrambling system, etc) without cluttering the overall 4 tiers of rated terrain.
Some AllTrails comments for what I’d consider NFS 3 / T2 terrain on a 2.5 mile loop with less than 300 feet of low grade elevation gain change:
Little Cranberry Lake Inner Loop, Washington - 288 Reviews, Map | AllTrails “This trail is NOT easy. There are many tree roots and sharp rocks on the trail with barely any sections that are even and easy. Wear good boots and if you’re a beginner (like me)… do NOT go alone. The scenery IS beautiful…”
Little Cranberry Lake and Trail 100 Loop, Washington - 394 Reviews, Map | AllTrails “Not an easy hike, probably moderate. Trails nearest lake are rocky. Trail through forest easier. Beautiful hike.” and “Rated as an easy hike. I would say it’s near moderate due to roots and rocky terrain. Experienced hikers will breeze through it, but novice hikers beware of your footing. You may take an involuntary bath in Cranberry Lake.”
This shows a clear “casual hiker” appetite for some way of showing that while a hike is “easy” from say a physical fitness / endurance standpoint (ala the much earlier Sierra Club system) that isn’t how people solely view difficulty.
The NFS trail development classification for C3 “Obstacles may be common, but not substantial or intended to provide challenge” would probably map to 1.5 / uneven ground, but there are also plenty of Class 1-3 trails that happen to pass through terrain without natural obstacles, regardless of development. Class 1-2 obstacle wording would probably put it into 2 demanding / 3 scrambling territory, but there’s no way of knowing which, and many examples show obstacle less terrain that is just undeveloped or infrequently maintained.
I honestly had never thought too much about the the T1/T2 level distinction until recently, but it has some significant merit.
It isn’t that unusual for NFS/NPS trails sometimes enter T3 terrain, and while they tend not to have “full” T4 terrain there can be mantles & drops that are more than just “using your hands for balance” T3, or fatal exposure on simpler terrain. Regionally in the US there are a number of trails that are legitimate T4+ from government land managers - someone on the east coast (hardly alpine terrain lol) was sharing some examples of them in the slack trails working group a while back.
I find “mountain hiking” terrain in the desert pretty regularly, and while I (typo edit) don’t agree that the word alpine can’t be used because it only exists in the alps I don’t think that values should have a specific biome associated with them.