[Talk-GB] Classification of roads

[Mark Goodge]

On 19/08/2021 18:35, Colin Smale wrote:
> There is a legal distinction between Tertiary and Unclassified; the 
> responsible highway authority decides, and records it in their 
> definitive list of streets. A tertiary road has a number, usually 
> prefixed by a 'C', which is not usually publicised.
> 
> Looking at Streetview it looks like Alexandria Road has a function for 
> through traffic, so IMHO it should not be tagged as residential. Whether 
> it's tertiary or unclassified depends formally on the HA as mentioned 
> above. But one thing is certain: the mere presence of houses along this 
> road is not sufficient to class it as residential.

OS OpenRoads has a "road function" column which indicates the usage of 
the road (as distinct from the "road classification" column which shows 
the legal status. The possible values of "road function" are:

Motorway
A Road
B Road
Minor Road
Local Road
Local Access Road
Secondary Access Road
Restricted Local Access Road

The top three obviously reflect the legal status of classified roads 
(and, if that value is present, is always the same as the "road 
classification" column), but the rest are an "on the ground" observation 
of how the road is actually used in practice. Broadly speaking, "Minor 
Road" corresponds to OSM's "tertiary", and, in urban areas, "Local Road" 
corresponds to OSM's "residential".

These are only OS's opinion, not a legal status, so there's no need to 
follow them slavishly if our own on-the-ground observation clearly 
points to something different. But they are open data, so we can use 
them, and they do form a useful guide when local observation is 
potentially inconclusive or ambiguous.

In this particular case, Alexandria Road in Ealing is labelled "Minor 
Road" by OS, so I would be inclined to agree that "tertiary" is the best 
option for OSM.

Mark