[Talk-us] Road classification

[Peter Miller]

I am based in the UK but have also done some remote editing of US  
data. The UK is of course the basis of the classification terminology  
used by OSM for historical reasons.

The key thing from my side is to ensure that the order is retained, ie  
a motorway should have more capacity and probably flow faster than a  
trunk etc etc. This is essential to allow routing engines to use the  
best road available. The proposed scheme does that. The initial coding  
of interstates as 'secondary' did not. There is always some  
subjectivity involved, but it will be good of the approach is  
consistent across the country.

I agree that both motorway and trunk roads should generally be free of  
traffic lights etc. The difference in the UK between the motorway and  
a trunk road is legal, the speed limit is different and motorways  
always have a higher spec, always have ramps, never have roundabouts.  
I was not able to determine when I should use Trunk and motorway in  
the USA and tended to use motorway.

Primary roads seem to me to be the core tag for major arteries in  
towns (or countryside) where there were multiple lanes but also have  
side roads, traffic signals etc.

Secondary and tertiary roads are really very pretty minor in the UK.  
In urban areas they are the roads that would feed multiple residential  
roads and residential roads would tend to not be through-routes.

Here is an area I spent some time on in Foster City and the  
classification of roads seems to have stabilized over the past month  
or so. Motorway for everything with ramps, Primary for the big road  
with traffic signals and then secondary and tertiary to make sense of  
local circulation in residential areas. I didn't see any place to use  
highway=trunk
http://openstreetmap.org/?lat=37.5413&lon=-122.2661&zoom=13&layers=0B00FTF

I seem to remember that it was me who made Skyline Bvrd a trunk road  
here (http://openstreetmap.org/?lat=37.7233&lon=-122.4942&zoom=14&layers=0B00FTF 
) . It seems to have stuck, but I am not sure if others would agree  
with that. It does seem odd for a trunk to turn straight into a  
secondary when it takes a lot of the same traffic towards the north  
although if most of the traffic heads up Great Hwy then that might be  
appropriate.

Here is a map I have just done showing the use of highway=trunk in the  
USA which is interesting and shows the very uneven adoption of trunk  
across the country. There are pockets where it is being used a lot and  
areas where there is no use of it.
http://www.flickr.com/photos/itoworld/3113029093/

Out of curiosity I have also added images for the other main road  
classifications:

motorway: http://www.flickr.com/photos/itoworld/3113880022/in/pool-itomedia
primary: http://www.flickr.com/photos/itoworld/3113885464/in/pool-itomedia
secondary: http://www.flickr.com/photos/itoworld/3113063009/in/pool-itomedia

I think the main message from these images is that the motorway tag is  
being used reasonably consistently across the country, the trunk road  
tag is only being used in pockets. Primary is used a lot especially in  
the east where it seems to form a complete network which is doesn't in  
the west. The use of secondary seems to be somewhat dependent on some  
arbitrary boundaries; are these state boundaries?

I hope that is useful.

Btw, do subscribe to our Flickr itomedia group (http://www.flickr.com/groups/itomedia/pool/ 
). We release images on a regular basis and are happy to take requests  
for bigger areas. Do also use OSM Mapper ourselves to make your own  
images at the city level:
http://www.itoworld.com/static/osmmapper


Regards,



Peter Miller
ITO World Ltd
www.itworld.com


On 16 Dec 2008, at 17:01, Russ Nelson wrote:

> mapboy at att.net writes:
>> A motorway is a four+ lane, limited access, grade separated
>> freeway.
>
> Like an Interstate.
>
>> A trunk is what a motorway becomes when it loses one of it's  
>> criteria.
>
> Like NY-17 used to be (haven't driven on it in twenty years, so maybe
> the grade crossings have been eliminated), or like the Taconic State
> Parkway.
>
>> A primary road
>
> As is US-11, particularly relative to Interstate I-81.
>
>> A secondary road moves traffic within a city. It would service only
>> a certain area within a city.
>
> Mmmmmm, this is somewhat ambiguous.  You could have a limited-access
> highway which only moves traffic within a city; example I-2XX
> highways.  What are the criteria for secondary roads outside of
> cities?  For example, what is US-11B, or US-11C ?  They are roads
> equivalent in quality to US-11, however they are bypasses; are they
> primary or secondary?
>
>> I hope this clarifys things for some users. I know it's not going  
>> to please those who have already used other classification schemes.
>
> IMHO (I may be wrong), but the solution to these quandries is: Use
> More Tags.  The more tags you use to accurately describe a road, the
> less important becomes the "highway" tag.
>
> -- 
> --my blog is at    http://blog.russnelson.com   | Delegislation is a  
> slippery
> Crynwr sells support for free software  | PGPok | slope to prosperity.
> 521 Pleasant Valley Rd. | +1 315-323-1241       | Fewer laws, more  
> freedom.
> Potsdam, NY 13676-3213  |     Sheepdog          | (Not a GOP  
> supporter).
>
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