Is this the correct term for a grade seperated road with two single lane carriageways? I know these are very rare and certainly offer nothing over an S2, except reducing the risk of a head on crash, but the road from Calderbridge to Sellafield Main Gate has been D1 for decades. I was driving on this yesterday for my Christmas dinner and believe the only reason this otherwise narrow and completely useless road is D1 is to reduce the risk of head on crashes, particularly involving lorries carrying nuclear waste.

A D1 doesn't have to be grade seperated either! can just be a Dual Carrigeway. There are a few photo's of D1's on the wiki i believe if you want to see some more examples

The phrase "single-lane dualling" is used in this bit of the DMRB in relation to a locally D1 stretch of a generally S2 road at an at-grade priority junction.

I think this may be the only reference to D1 roads in the DMRB. Other people around here will know much better than I do.

Offhand I can only think of one example of D1 on a modern major road but not at a junction: the swing bridge on the A63 Selby bypass.

Purpose-built ones are very rare, but there are plenty formed by hatching down a former D2, such as this one in Glasgow from Truvelo's site:

The Sellafield one is clearly a single track road that has had another carriageway slapped down alongside it. There's no need for a D2 in and out of there.

It's always been an interesting one as the other two gates have wide, purpose built S2S approaching them. I can only think it was done for the lorries and most people I know who work at Sellafield use the North Gate and only really use Main Gate if North Gate is too busy.

I'm unsure as to the exact date of the single lane dualling, but the southwest facing one will be the original one - it serves a number of buildings including Sella Park which dates back hundred of years, as well as two former farmhouses, High House Farm and Yottenfews farm, that still exist near the North Gate. In fact the present location of that gate only dates back to the late 1980s, prior to that it was further south, with a further section of road where online D1 dualling of a former single track road had taken place to another now demolished former farmhouse near the old gate.

There was an improvement scheme in the mid eighties that saw a roundabout built near Yottenfews and a new access road designed to effectively by pass Beckermet for traffic from the north. I do think the D1 predates all this as I have been living in Cumbria since 1974 and the junction at Calderbridge always led to a dual carriageway, of sorts.

The access road to Dounreay seems to be a D2 that ends on a Give Way to an S2. Can't be many of them about!

Here's a D2 giving way to an S2, with the S2 becoming a motorway slip road!

Before the M67 was built, the D2 A560 gave way to the S2 A57 at Hattersley.

Before the A1(M) was built, the D2 A414 (which may have been A405 at the time??) gave way to the S2 or S3 A1 at what is now J3.

There's this example in Rugby which I've always found odd...

http://maps.google.co.uk/maps?f=q&sourc ... 97,,0,7.21

There's an interesting D1 on the B946 through Newport. It's more of a novelty caused by two parallel one way streets than a proper D1 but I like it all the same.

I'm sure it probably dates back from when the ferries were still running and at the other end is a mini-roundabout that I've never worked out the point of.

There are quite a few examples of a dual ending at a T-junction with a single, although I suspect Give Ways are rare. One that spring to mind is the A663 Broadway/A62 Manchester Road in Failsworth.


And the A560 through Hattersley is now a classic example of a "modern" D1

The worst thing about that road is looking in the opposite direction from where I took my picture where this bus stop is deliberately designed to obstruct traffic whenever a bus is stationary

And for streetlighting fans those Alpha 4's on ancient trolleybus poles shown in my picture have been replaced.

There's another in Luton, this time minor residential streets, at the end of Mayne Avenue. Why the need for D2, I've no idea. Each carriageway even has doubled up speed cushions.

I originally thought of that one, but didn't mention it as the A62 is S4.

Only sort of - most of it is now S2. There's a few bus lanes around there though.

I wonder how many examples there are of purpose-built D1 B-roads

The A9 at Bankfoot has 2 D1's to stop people making right turns.

There is also this one on the Isle of Mull, this must be one of the remotest dual carriageways in Britain.

Is this a D1-and-a-half?