(EDIT: After feedback from others, and a more careful reading of the wiki, I think a different scheme is better suited to this area, and I'll post details soon)

I've been using my GPS-enabled Android phone to trace the various trails in the Middlesex Fells Reservation outside of Boston. This is a document specifying how I've been laying out the attributes. This is mainly for my own reference, so I can be consistent as I make progress (my goal is to get all trails into OSM over the next year or so). But, if anybody wants to chime in with any corrections or suggestions, I'm all ears. Thanks!

I'm classifying the trails on two dimensions: official status, and actual physical characteristics.

As far as the actual, physical characteristics go, here are the descriptions I've got for the trails I've seen so far:

* Car-ready roads: There are a few "trails" which a regular passenger car could use without issue (of course, this is prohibited in real life). These are graded, and are usually hard-packed dirt or gravel, although they may even be paved in sections. These get "highway=service", "motorcar=no", and "motorcycle=no" tags.

* 4x4 roads: These are impassable by a regular car, but could be used by a 4x4 truck. These get "highway=track", "motorcar=no" and "motorcycle=no" tags.

* Paths: No motorized vehicle can pass, perhaps because the trail is too narrow, or too windy, too rocky, or too sheer and steep. These get "highway=path" (which implies no motorized vehicles).

Now, for official status. This park is run by the Massachusetts Division of Conservation and Recreation (DCR), which was formerly the MDC. The DCR disallows decides which users get to access which trails. They prohibit all motorized vehicles entirely, and they have the following trail classifications:

* Off-Limits: Trails that are "too close" to the reservoirs may not be used by any member of the public, at any time. Yet, there are trails here, as seen on DCR maps posted at various parking areas. These all are getting the "access=no" tag. (obviating the need for any "motor*=no" tags)

* Fire Roads: The condition of these trails varies wildly, from paved and wide, to rocky and narrow. Regardless of condition, the DCR allows all park users (including bicyclists) to use these trails. 4x4 roads and paths get the "bicycle=yes" tag. (bicycle access is implied for car-ready roads).

* Designated Trails: These trails are officially marked with colored blazes and sometimes wooden signposts. Hikers are allowed to use these trails, so these all get the "foot=designated" tag. Bicycles are not, in general, allowed to use these trails, so the "bicycle=no" tag is applied to the car-ready and 4x4 roads (bike restrictions are implied for highway=path). The exception to this is for those sections designated as being on the "Mountain Bike Loop". All of these get the "bicycle=designated" tag.

* Undesignated Trails: These trails are officially unmarked, and appear on no official DCR maps. In some cases, these trails were previously designated, and you can occasionally find the remnants of very old blazes. The DCR does not explicitly prohibit hikers from using these trails. These are all paths, impassable to vehicles, so they all get "highway=path", which implies only foot access. So, no need to add any tags for this case.

The DCR also recognizes a handful of named trails (e.g. the "Skyline Trail" and the "Reservoir Trail". These each have their own color blaze, and they snake around the park, following various roads and paths as they do. Sometimes more than one named trail will be on the same path at the same time. I've done these using relations. So, a way will get marked with the attributes listed above, and, if it's part of a named trail, it will also get an association.