[OSM-talk] Korean roads and highways

Alex Mauer hawke at hawkesnest.net
Wed Aug 15 22:26:49 BST 2007

Tom Hughes wrote:

> I used trunk there rather than motorway, on the basis that in most
> countries motorway is a very specific legal classification and I don't
> think any US highway would ever meet that standard? if not then by all
> means use highway=motorway with an appropriate ref tag.

I believe the US "freeway" or "Interstate" meets, or is a close enough
equivalent to the motorway designation. (I assume the precise
specifications for a motorway varies between european countries as well...)

There are three or four major highway systems in the US: the Interstate
highway system, commonly called the freeway; the US highway system; and
the various state highway systems.  In addition, there are individual
county/parish highway systems within each county.

I've been using motorway for any limited-access, dual-carriageway,
grade-separated road.  (This includes all interstate highways and many
US highways).

I've been using trunk for any dual-carriageway, high speed (speed limit
65+ mph), non-grade-separated road (this includes many US highways and
some state highways).

I've been using primary for any US highway that does not meet the above
definitions for motorway or trunk.

I've been using secondary for any state or county road that doesn't meet
the above definitions for motorway or trunk (As far as I know, no
county road meets those definitions)

And I've been using tertiary to designate any sort of "significant" road
that isn't any of the above, where "significant" is purely a judgement call.

There are a few places where I see problems:
In the US, the designations primarily describe who maintains the roads
(where the funding comes from).  Interstates and US highways are
maintained by the federal government, state highways are maintained by
the state, county roads by the counties (presumably this is obvious).

As far as I know, the only designation which requires meeting a certain
standard is the interstate. A lot of US highways and some state highways
are built to interstate standards without being designated as an
interstate.  A lot more are built "nearly" to interstate standards,
leaving out some of the required features (e.g. overpass bridge height
may be too low, entrance/exit ramps too short, curves too sharp,
occasional non-grade-separated crossings etc.)

What this means is that some US highways are built to a lower standard
than some state highways; some state highways are built to a lower
standard than nearby unclassified roads.  On the other hand, some US or
state highways may be built to the same standards as an interstate.

Also, interstate, US, state, and maybe even county highways may share
the same  physical route for part of their length.  Usually this happens
when one of the routes already built nearly to interstate standards is
upgraded to meet those standards, or when two state or US highways
follow a route that's close enough that it makes more sense to combine
them.  Some portion of the route will be classified as being a US
highway; the state highway designation is not removed.  The same can
happen with two different US or state highways, where a portion of two
highways follows the same physical route.

This also means that a "US highway" may change several or many times,
from a motorway or almost-motorway all the way down to a 2-lane
residential street.

I hope this description sheds some light on the US highway system for you.

The route-sharing seems to be one of the most significant differences
between the roads of the US and UK; am I correct to think that each
section of road in the UK is given one designation, and not multiple?
That is, the situation where US 41, I-43, and I-94 are all on the same
section of road, simply would not happen in the UK?

-Alex Mauer "hawke"

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