[Talk-us] United States Roadway Classification Guidelines

[Alan Millar]

>> >> set of guidelines at:
>>
http://wiki.openstreetmap.org/wiki/United_States_Roadway_Classification_Guidelines

I read the whole page, and this is the first comprehensive narrative I've
seen that makes sense to me for mapping highway tags on US roads.  This is
a good proposal.  It looks clearly like more of a process description than
a hard definition of tag values, but I believe that is necessary for the
highway= tag in the US.

>    The proposal linked here suggests that mappers tag roads classified
by
> the government with certain highway= tags. 

I didn't get that interpretation from it.  The proposal qualifies govt
classes as "for the first iteration", followed by further rounds of
re-evaluation and refinement.

>    But that doesn't mean a two lane at-grade
> highway should be coded the same in one area as a four lane limited
access
> highway in another.  

Agreed, but I didn't read such an extreme disparity in the proposal.  

In contrast, a two-lane at-grade country highway in one area *should* have
the same highway= tag value as a 4-lane urban boulevard in another area,
when neither are limited-access freeways nor residential streets but do
have similar local significance.

>> We have those tags: lanes=*, width=*, etc. But there's no "on the
>> ground" definition of importance,
> 
> Yes there is. It's the highway= tag.

I think the point is that the highway tag is *not* an "on-the-ground"
definition, because you can't go out to every road in the US with a camera
and measuring tape and say "This sign or measurement right here tells me
exactly that this road is a primary/secondary/tertiary".  Some values are
pretty clear, such as motorway and residential.  But others only have
general correlations, such as a US highway is likely or often a primary or
secondary, or a county highway is likely or often a secondary, and a big
suburban street is likely or often a tertiary.  But there is no exact
measurement of importance, so it is subjective.

But that is OK.  The highway tag doesn't NEED to be an exact on-the-ground
measurement or classification.  It needs to be a one-word summary that most
people will find useful for navigating through the area by car, bike, or
roller-skate.

Further clarification of the road, such as government classification and
detailed physical properties, should come through other tags *in addition*
to the highway tag  (ref=, lanes=, width=, surface=, access=, route
relations, etc).

>> and there's nothing wrong with
>> tagging correctly for the renderers.
> Yes there is. "Tagging for the renderers" is the first thing people in
OSM
> will tell you *not* to do.

OK, now this is getting silly.  People are told not to tag *incorrectly*
to force a particular appearance from the renderer.  Nobody is told not to
tag *correctly* when it matches what people want to see rendered.

>> Classification has been
>> subjective from the beginning in the US, because there is no
>> consistent government-assigned classification.
> That is incorrect. There is a relatively consistent government-assigned
> classification system.

There is one US federal, fifty state, and a thousand county classification
systems, and they don't consistently define road standards across the
entire country.  Only US Interstate is pretty clear and unambiguous.  
"Classification has been subjective because..." means that you can't take
any government-assigned classification that we have in the US (US highway,
state highway/state route, county highway/county road), and say it *always*
reasonably determines useful values of
highway=trunk/primary/secondary/tertiary.  It can only be a good starting
guess, no more.

>  The suggestion I made
> in my first reply to this thread was that we use a separate tag to
describe
> what the US government calls the way. 

I think most everyone agrees.  It is mostly reflected already as the ref=
tag or a route relation.  I don't think most people would object to
additional tagging for it.

You know, I think people are more in agreement on the whole subject than
it appears from these discussions.  The emails look like a lot of
disagreements, but perhaps it is more wording than actual disagreement on
the ideas and substance.

- Alan

--
Alan Millar       am12 at bolis.com