[Talk-us] Gravel roads and surface tags in the US

[Kevin Kenny]

On Thu, Apr 19, 2018 at 10:53 AM, Max Erickson <maxerickson at gmail.com>
wrote:

> >I grew up in an area with these kinds of roads and I don't think
> >they're technically compacted.  The gravel, which is crushed
> >limerstone, is laid down and due to its chemical properties creates a
> >smooth surface after several months of traffic.
>
> Having read about this some since Tobey mentioned it on Slack, the
> compaction is often meant to come from traffic.
>
> In the Midwest the material is often from local "gravel pits" which
> are glacial material, so a mix of sand and rounded stone. I think they
> do some sorting and remixing of the material before using it for road
> surface construction, and they definitely add clay as a binder.
>
> I think the use of clean stone (the wiki gravel) is more common for
> ornamental driveways than for any road meant to bear much traffic.
> Apparently part of the issue is that there aren't many built roads in
> the UK (and Europe in general) that aren't sealed.
>

Exactly - I'm guessing that we're once again dealing with something that's
familiar to us but nearly unheard of in Europe.

Around here, the native rock is sedimentary and ranges from limestone to
limy shale to various sandstones and conglomerates, that is then highly
sculpted by glaciers and water - both above and underground, the terrain is
karstic. Lots of rural roads are laid in crushed stone - which tends to
include everything from the above mix except the good limestone, which is
too valuable as a cement feedstock. (It has just the right trace minerals
to make high-quality hydraulic cement.) The material is both limy and
clay-ey enough to make it both aggregate and binder.

Across hilltops, the woods roads are often enough made simply by scraping
away the topsoil, which might not be more than a few cm deep, and exposing
the native shale. It's flat enough to drive on, and spallation makes both
aggregate and fines for a natural macadam.

There are also roads in some of the old fishing communities down at the
coast that are paved in crushed oyster shell. That's again a material
that's limy and prone to spallation, so again provides both aggregate and
binder. (I suppose it's the same stuff, only Holocene rather than Devonian!)

None of these are sealed. Once the snow is gone, the highway department -
or the landowners - will come through with a grader and maybe a truck or
two of fresh aggregate, smooth out the frost heaves, clear the rock slides,
and let the traffic compact the surface again.

They do run to being dusty in dry weather, and some of them aren't nearly
as well drained as they might be.

The locals call them 'dirt' roads, but they are definitely an improved
surface - the better ones are safe to drive on at 50 km/h or so.

I've been tagging them 'surface=compacted', but recognize that it's
controversial. None of the Wiki categories fit properly, making me suspect
that this sort of road doesn't exist in the places that the Wiki editors
(so far) are familiar with.

Even what to put in 'highway=*' is controversial for some of these. Some
that I'm familiar with are most definitely highway=tertiary at least.
Labeling them 'highway=track' is surely not correct when they are the main
roads into and out of the settlements they serve. Wiki agrees with me here:
'track' refers to agricultural or forestry use, not to the quality of the
road surface.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/talk-us/attachments/20180419/3d1a5937/attachment.html>