That’s very interesting
@Matt.GC; thanks for posting!
If you don’t mind me tapping into your SABRE knowledge for a second, I’d like to ask a few motorway questions.
Firstly; what’s actually the difference between dual carriageway standard and motorway standard other than that you can turn right on a dual carriageway and have slow vehicles driving along it? I quite frequently drive along the stretch of the A40 dual carriageway between Raglan and Ross-on-Wye during my driving lessons (indeed, my first driving test route took me along it, from Monmouth in South Wales to Whitchurch in Herefordshire), and I can’t see much that would differentiate that stretch of road from some motorways. It has a central reservation, it has two lanes in each traffic flow direction, it has slip roads at each junction, and it has motorway staples like service stations. Yes, it only has two lanes in each direction whereas some of the big motorways (e.g. the M4) have three or four, but my nearest motorway, the M48 between Magor and Bristol, also only has two lanes in each direction along its entire length. I’ve never been along it personally, but I believe that the M50 between Ross-on-Wye and Worcestershire, another motorway that isn’t too far from me, is similar if I’m not mistaken.
Secondly, are there “tiers” of motorway, if you like, with some being maintained and built to a slightly higher standard than others? On the motorway map posted earlier, I noticed that the major ones like the M4 were highlighted in bold blue, whereas the more minor ones like the M48 were not. I also ask this question because as I said above, many of the more minor motorways seem to have things like less lanes and different lengths of slip road. The minor ones also never seem to have had the smart motorway upgrade, and the general standard of maintenance seems to be a bit lower. For instance, the entire M48 through Wales is now capped at 50mph for the foreseeable future due to defective barriers, and there’s no sign of those being fixed any time soon.
Very interesting question. Again it has historical meaning rooted in this country's laws around rights of way. So the A40 you mentioned? Well if you wanted to you could ride along it with your push bike, on horseback or even walk along side it as long as you aren't blocking the public highway or doing anything deemed as dangerous. Roads pre-date cars, before cars people would walk or ride horses along them. So this presented a problem in the 1950's when the government wanted to build high speed limited access highways (it's actually where the name Motorway comes from, to distinguish a road for motor vehicles only from that of all access roads). So parliament passed the Special Roads Act.
The Special Roads Act meant that for the first time in this country, roads could be designated as special roads with limited access that did not give everyone an automatic right of way. All motorways are special roads. Hence the restrictions. All of them are controlled and maintained by the national highways agency and not local authorities.
A duel carriageway is just another design of road. Some are built close to motorway standard but most are not. There are strict rules around motorway standards but there are some exceptions. For instance, there is actually a single carriageway motorway (I think it's near Manchester?) because any road without an escape route, that leads directly on to a motorway, has to be classed as one itself. So if you see an odd kind of motorway, it's likely a project that was unfinished or cancelled at some point. As for ones like the M50, it is one of the oldest motorways in the country. It was actually built to motorway standard at the time, but standards then improved in the 1960's and 70's. Many important routes like the M5 (which was built at the same time between Ray Hall and Strensham and terminated at the latter, hence why the M50 even exists to continue talking M5 traffic towards Ross) were upgraded to higher standards. You may notice the sharp corners on the M5 as you get closer to Birmingham and the hard shoulder drops under bridges? That's because it was built to lower standards originally, as dual 2 lane and has been upgraded. The M50 is not an important motorway so has never been upgraded but still keeps it's status.
The Preston bypass, now part of the M6, was the first motorway in the country (not the M1, which was the first full length but contrary to popular belief the Preston bypass was the first). It opened as duel 2 lanes, with no central barrier (just a patch of grass that people actually used to stop and have picnics on!), soft shoulders which were just gravel and mud, and hideously low capacity grade separated junctions. It was shortly afterwards completely rebuilt , including every bridge and junction and is now double the width. Very little of the original remains at all (I think part of Samelsbury interchange is all that remains).
So to summarise as I'm waffling on, there aren't strictly tiers of motorways. All have the same restrictions unless otherwise stated, such as national dual carriageway speed limit, physical central barriers, no horse drawn carriages etc. Tiers only exist in how important that are really in terms of funding and design standards, hence why some can be D2 (like the M50) and some can be D5 (M25 near Heathrow). You mentioned the M48, this actually used to be the M4 across the Severn Bridge, but because it's only D2 it became hideously congested by the early 90's. Hence the Second Severn crossing (which actually isn't the second) and new route of the D3 M4, which I remember I went on a primary school trip to Severn beach to see being built. Both crossings are motorways, both are special roads, both are maintained solely by the national highways agency, both have the same restrictions unless otherwise stated, even though their widths and design standards differ.
The A40 you mentioned has likely been upgraded to higher standards over many decades to ease traffic congestion, but does not have a statatury instrument and is not a special road. It's likely partly maintained by a local authority. However to muddy the waters further, there are a few A roads that are designated as special roads but these are extremely rare. I think there's one up your way actually Matt. I'll have dig and edit the post with a link that explains it.
Edit: Here you go
@Matt N. One of the most interesting websites on the internet for saddos like me. This article explains special roads. Basically the short answer to your question is that the difference is in the designation of being a special road or not and not design standards, width, layout or anything like that.
https://pathetic.org.uk/features/special_roads/#:~:text=All motorways are Special Roads,t Special at all...
