[Talk-GB] Questions about highway classification

David Earl david at frankieandshadow.com
Tue Mar 9 11:54:30 GMT 2010

On 09/03/2010 11:29, Nathan Edgars II wrote:
> I'm currently trying to form a sort of consensus as to the best way of
> defining the classes of highway in the US, and a bit of information
> about the UK would help. I know about the definitions used
> (trunk=primary route network, primary=A roads, secondary=B roads), and
> have a few questions.
> *Is the tagging of motorway through secondary reasonably complete and
> accurate, such that OSM can be used to get a feeling of how dense the
> classes are and how they interrelate?
> *What's the difference between a motorway and a non-motorway built to
> motorway standards? I thought it was the ability to ban non-motorized
> vehicles, but apparently this can be done on non-motorways. Has it
> become simply a political distinction?
> *Are there criteria that the Highways Agency uses to define the
> primary route network (more specific than the general purpose of
> connecting major destinations) and the difference between an A road
> and a B road? Or are changes handled on a case-by-case basis?
> Thank you for any information.

This is a discussion that goes round and round.

But the convention most people adopt is "map what you see", so in the UK 
that is blue signs mean motorway, green signs yellow text means trunk, 
black and white signs means primary if the road number is A and 
secondary if B.

Some roads are designated e.g. A1(M) which *is* a motorway, but numbered 
rather oddly usually because it forms part of a longer road where parts 
are motorway and parts aren't.

Any road can have vehicles of any kind banned on it. But on motorways 
this is by definition (well, I think there still has to be a formal 
order to that effect) while on other roads this has to be implemented by 
a specific advertised and approved exception. Hardly any roads in the UK 
are built to motorway standards but not designated as such - usually 
they would be missing things like the emergency lane which is a normal 
feature of motorways (though they are beginning to row back on that in 
places where space and congestion are problems). Grade separated 
junctions don't make roads into motorways. The point about signing a 
motorway is that it is a name that tells drivers what rules apply, so it 
would be wrong to tag a road that looks a bit like a motorway (e.g. the 
A14 in Cambridgeshire or the A50 in Derbyshire) but where e.g. cyclists 
can use it.

The criteria are based on a now ancient "hub and spoke" design for road 
numbering which has been adapted over the years. It's complicated by the 
difference between trunk roads and other A roads, the nominal difference 
being whose jurisdiction they are, but even that has faded with the 
Highways Agency handing some trunk roads over to local authorities 
("de-trunking") without changing the signage and so on on the ground.


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