[Talk-us] "highway" tags in the US

Alex Mauer hawke at hawkesnest.net
Tue Mar 4 23:32:45 GMT 2008

Karl Newman wrote:
> On Tue, Mar 4, 2008 at 10:26 AM, Alex Mauer 
> Hmm... Then why are all the generic roads from TIGER marked as residential?

DaveH answered this one.

>     Other roads change speed as they enter urban places (e.g. primary roads
>     may go from 55 down to 25 to pass through a hamlet)  Why shouldn't
>     tertiary be the same?  It's all about the relative status of a road to
>     the roads around it.
> But the residential road is slow for its entire length, whereas your 
> hamlet example is only slow while in the town.

Regardless of speed limit (for which we have a separate tag anyway) 
there are some residential/commercial/industrial/rural roads which are 
more significant than the ones around them.  I see no reason to simply 
discard the existence of the tertiary tag just because it's a 
residential area which is being mapped, and because the speed limit is 
the same.  The speed limit is not the only distinguishing factor.

You appear to be suggesting that a road with a 25 mph speed limit cannot 
be tertiary, but a primary road can be 25 mph for part of its length. 
That doesn't make sense to me.

>     Hmm...it seems to me that perhaps you're writing this from a perspective
>     of "what a driver using the road might expect", while I'm coming from a
>     perspective of "how should this road be tagged".  Is that the case?
> "How should this road be tagged" needs to consider the expectations of a 
> driver/bicyclist/pedestrian. I've always been uncomfortable with the "if 
> it looks like a motorway, then tag it as such" for a couple reasons. 
> First, does it meet the standards for a motorway in terms of height 
> restrictions, turn radius, restricted access, etc. 

Yep, that's the question, "does it meet the standards?".  It's a hard 
question to answer at a glance.

> Second, over what 
> distance are you going to consider the road characteristics? Part of my 
> commute route follows a state highway that looks like a motorway in 
> isolated sections--dual carriageway, 60 MPH, restricted access, etc., 
> but it has stoplights at grade intersections every mile or so, sometimes 
> more often. Also, if you continue on the road, it peters out into a 
> 2-lane highway wit h slow tourists and grinds through pedestrian-clogged 
> tourist-trap towns. Not a motorway.

I would consider the characteristics over any portion of the roadway. 
To use your example, and assuming that by "restricted access" you mean 
"bicycles/pedestrians prohibited", I'd tag it as trunk for most of the 
length (the dual carriageway/high speed section) and secondary once it 
drops to two lanes.

There's no reason that a road must be tagged the same throughout its 
length; the state/county -> secondary, US->primary guidelines just give 
a minimum for those administrative classifications.  If a highway meets 
the relevant specifications it should absolutely be tagged as a 
motorway, as long as you know it meets them.  If it doesn't meet them, 
then the physical layout of the road (dual-carriageway, possibly ramps, 
etc.) as well as the speed limit tags and access restrictions give a 
hint to the map user how closely this will resemble a motorway.

-Alex Mauer "hawke"

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