I have now uploaded a summary of the figures for the UK coverage estimates as a CSV file here - http://www.reedhome.org.uk/Documents/OSMCoverage.csv
Several people have expressed an interest in seeing the proportion of named roads by local authority area. Those figures are included in the table. There is also a map here - http://www.reedhome.org.uk/Documents/OSMNamed.png The other figure that may be of interest is the proportion of roads that have been plotted, but not completely tagged. See the column labelled "Percent other" in the CSV file. These roads are not included in my totals, because I can't tell what type they are. Broadly speaking these are roads marked as "highway" with a type of "road" or "fixme". There are also a few that have been mis-tagged, for example as <highway:some street name> or with a combination of conflicting highway types. But these are a very small proportion of the total. Most are tagged <highway:road> which is normally intended to mean "I know this road is here, but I have not yet decided what type it is". The overall proportion of these is quite low, but it is surprisingly high in some areas - notably Luton, and Northumberland for example, where almost a third of roads that have been plotted are not fully tagged with a type. Lincolnshire, Suffolk, Somerset, Trafford, Norfolk and Wiltshire also show a high proportion (>10%) of roads that I can't classify. I thought that comparing the area enclosed by the admin boundary on OSM with the area published by national statistics would be a good indicator of whether the boundary was accurate. In practice it works sometimes, but not others. I think this is mainly because of how the coastline and estuaries are handled in different places. Bristol is the extreme -the government thinks it is about twice as big as the area included in the boundary on OSM. The CSV file also shows the breakdown between different types of road (motorways, primary, secondary, etc). I've not looked closely at this yet, but a quick scan suggest that the figures for primary roads and motorways could sometimes be a good indicator of how accurate a boundary is. For example, it looks as though the boundary for Luton on OSM includes a bigger chunk of the M1 than the DfT believes they are responsible for. Enjoy.
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