So you like the look of the Wiki, you want to help out, but perhaps you don't feel you know enough. This page gives some suggestions of where to look for more information!
A good first start with any research for the Wiki is to look at the area on old and current maps, and to compare the two. For these purposes, Sabre Maps is absolutely invaluable, as it allows you to compare a whole range of different maps without having to move!
If Sabre Maps isn't good enough for you, or you are looking for changes in the last 50 years, then you'll need to find actual maps or atlases as copyright prevents such maps being offered online. E-bay, and similar sites are a good starting point for getting hold of such maps, as are local secondhand Bookshops. Also take a look at Category:Road_Mapping to get a feel for the different types of maps available, if you don't already know.
If you are still struggling, then all is not yet lost. Take a look at modern OS mapping, either online or on paper. They will often show up laybys and Oxbow Roads, showing new alignments and so on. This can be checked on Google Maps / GSV.
One of the frustrating things about researching roads is that there are very few books on the subject. Places like the Scottish Highlands are comparatively well covered, thanks to the roads constructed by Generals Wade and Caulfeild and Thomas Telford bearing interest to wider spectrum of historians. The Motorway era is not yet really seen as 'history', and other roads have generally just developed over centuries.
Roman Roads are reasonably well covered, as are historic bridges, but again it will take a good rummage in secondhand Bookshops or local libraries to discover useful information.
Unfortunately, due to the very nature of the Sabre Wiki project, if you are researching a road then you will often find that the Wiki is already the most comprehensive online resource for it. Sabre Member sites also offer information on a range of routes, but be careful to complement them rather than duplicating!
For specific features of a route, especially bridges, a quick Google will often reveal some useful information. If the bridge is listed then the listing report will appear (several times). Depending on the site as to how much data is provided, some have images, maps and contributor notes, others just the bare listing. Local community websites will also sometimes offer information on bridges.
Junctions and the roads in general are less well covered, however, sites such as Hansard can provide dates for re-alignments and upgrades. For more recent projects, the contractors will often still have data on their own websites.
Explore for yourself
At the end of the day, the best way to learn about a stretch of road is to go and take a look. Now, obviously this isn't always possible - no one is expecting someone in Kent to take a daytrip to Shetland to write up the Wiki pages on Shetland's B roads, but there are closer roads to take a look at!
Driving a route can give a basic feel for a road. It is certainly enough to write a route description - especially if you use maps / GSV to jog your memory! However, if you are wanting to create an article of more depth, or expand an existing one, then the only way is to walk or cycle at least parts of the road. This gives the opportunity to stop where there may not be somewhere convenient / safe to park, take photos, nose around in the undergrowth and generally understand the route. However, beware as this can take a considerable amount of time. The A82 page is still incomplete in the full detail sections, but has already taken about 15 separate days or part-days of investigation to get this far...
Of course, if you want to go and take a look at something, there is nothing stopping you from proposing a Sabre Awayday or Roadtrip to make it that bit more interesting!
Hardcore research : In the archives
If looking for a historical route on the ground isn't quite enough, and you've got enough time, patience and stamina, then for serious hardcore researchers, a trip to one of the archive facilities in the country might be in order!
The National Archives (TNA) in Kew have a large collection of files relating to many road projects. A lot of information relating to the 1935 Road numbering revision, for instance, has been obtained from TNA. You will need to obtain a reader's ticket before entering, but access is generally available to anyone. You can take a camera along to photograph archive documents, or use some of the in-house camera facilities, which can be emailed to you. Be warned - archive facilities are a "dumping ground" for material and finding useful information can be quite hit-and-miss.
The National Archives are now actively supporting SABRE and in particular directing road history related questions to us.
The National Library of Scotland in Edinburgh have a substantial collection of maps that can be digitised (in order to appear on SABRE Maps). Viewing is by appointment only, but they are also supportive of SABRE and have kindly given us permission to host historic maps from their archives.
Other than the relevant national bodies, most top-tier local authorities have their own archives, though some do share. These archives often share readers' tickets (called CARN tickets), and their quality can be rather hit-and-miss. As an example, the Mitchell Library in Glasgow is a dream of an archive, full of helpful staff who can't do enough to help. At the other end of the scale is Birmingham City Archives, who don't even appear to hold documentation regarding the A38(M), and who supposedly hold the records of the former West Midlands Metropolitan County Council - though WMMCC's records are completely unindexed and stored by Wolverhampton City Archives for their fellow archives! It's also worth bearing in mind that as local government bodies have been reorganised on a random basis since 1965, the documents for a particular area might be in a neighbouring authority's Archives...