Where is it?
The point where traffic heading to Newcastle and the surrounding area forks, choosing between the coast and Tyne Tunnel or the Western Bypass and city centre. The A1231 provides access to the large populated area to the east of here, including Sunderland and Washington.
What's wrong with it?
Its primary function, to either split northbound traffic from the A1(M), or merge it heading south onto the A1(M), works just fine. The trouble is the horrific connections with the A1231. As a major road, dualled and grade-separated and providing access to Washington, Sunderland and Middlesbrough via the A19 from the A1 Western Bypass, the connections are laughable.
Thankfully access is provided to the Western Bypass. To get there from the A1(M) from the south, leave a junction early and traipse through Washington on the A195. To get there from the A194(M), leave a junction early and do the same on other roads. To get between the A1 and A194(M), the same must be done. In effect Washington makes many connections this junction ought to have.
Why is it wrong?
Presumably the A1231 came much later than this junction, which was built along with the A1(M) in the early 1960's. The Western Bypass is newer, though the junction already existed as the start of a dual carriageway into the centre of Newcastle. When the A1231 was added one can only assume money or land wasn't available to make more connections, or it was thought no others were needed.
What would be better?
It's reasonably simple to add a new sliproad from the A194(M) southbound to the A1231 eastbound, and space is also available for a loop from the A1231 westbound to the A194(M) northbound. However, given the additional distance to reach this junction to make a direct connection, it's more likely traffic would continue using Washington as a rat-run and so the investment is probably not worth it.
Right to reply
I go up the A1 to get to work in Dunston, and I suggest the main reason why this junction gets clogged so much is not the junction itself, but the fact that the A1 is only two lanes from the A167 to the Coal House Roundabout (next junction to the northwest, providing access to Team Valley Retail World).
Widening this road would really be a problem, because this section crosses the East Coast Main Line...
I wrote a spirited defence of Junction 23 of the M25 the other day, but I 100% agree with you that this one, at the other end of the A1, is a shocker.
The only thing to be said in its defence is that 90% of its traffic probably uses it only for its primary functions, which, as you say, are to merge or split the A194(M) and the A1(M). Relatively few people will actually try to use this junction to link to or from the A1231; the road planners, in their defence, would probably say that this was never the purpose of the junction. However if you do try to use the one viable connection between the motorways and the A1231 - i.e. to come off the southbound A1(M) and join the 1231 Eastbound - then you're sure to enjoy the hairpin sliproad and dive across the lanes that this route involves.
Your write-up makes relatively little reference to the tribulations of using this junction for its other purpose - providing passage between Birtley and the motorways. Again this route is characterised by incomplete connections - you can come off the A1 southbound to Birtley, though this involves doubling back at the roundabout where the A1231 terminates; and you can get from Birtley to the A1 northbound via a slightly odd, sharply curved sliproad off Portobello Road; but you can't do anything else.
The interesting subtext to this junction, of course, is that both of the motorways involved have, in the relatively recent past, been the A1. The Gateshead/Newcastle Western bypass, via the Metrocentre and the Blaydon Bridge, currently holds that title, but not long ago (as recently as the early nineties I'd guess) what is now the A194(M) was the A1, heading on through the Tyne Tunnel. Additionally, what is currently the A167 - crossing the Western Bypass one junction north of here by the Angel of the North, then continuing through Low Fell, Gateshead town centre (bisecting another Bad Junction, I believe), the Tyne Bridge and the Newcastle Central Motorway - was in fact the original A1. It would have continued to hold that designation, too, had the grandiose schemes of T. Dan Smith (whose vision for a "box" of motorways enclosing central Newcastle merits an article in itself) been fully realised. As it was, Smithy gave us the Central Motorway, which with its fast-lane merges, howling double-decker sections and bits of flyover heading nowhere, is more than quixotic enough to keep the fan of weird roads occupied for quite a while.
You are correct - the A1231 Sunderland Highway was built much later than the rest of the A1231 (or B1288 as-was).
I'm from Birtley and I can vaguely remember the A1231 Sunderland Highway being built in the 1970's - prior to that the Mill House Roundabout (at the top of the map)simply linked Portobello Road (where the A1 South exit sliproad joins), the Eighton Banks/Wrekenton road and the B1288 towards Washington (past the Mill House pub). Interestingly, part of Portobello Road has been renamed to the A1231 at some point in the recent past - it was always the B1288 when I was a kid - presumably so traffic from Washington stays on the A1231 as it filters onto the A1 northbound.
The Mill House roundabout is now covered in traffic lights, as is the A1 southbound exit sliproad. The southernmost A1231 roundabout (where sliproad onto A1 North is) used to be a simple gap in the central reservation - the roundabout was built for the Truckstop that was built next to the roundabout in the mid 80's - now demolished. Am I showing my age?