Heres another just off jc 26 m5, they have painted new lines now making it just two lanes
maps.google.co.uk/maps?f=q&sourc … 1&t=k&z=18
Before the advent of the M5, when the A38 used to carry all N to SW traffic, there were long stretches of 3 lane road from Quedgeley (Gloucester)to Filton Church (Bristol) with short stretches of 2 lane interspersed. This road was known as “death alley” in the 1950s and '60s and was the most notorious stretch in the country.
There’s one off the M4 for Magor (Tesco & Wilkinsons), a bit sill really on there I have often had to brake on those stretches.
Before they stretched the M4 the A48 between Cardiff & Swansea had a central suicide lane, handy for a game of chicken
BigJon:
The A465 Heads of the Valley road at Abergavenny definitely used to be like this, I remember driving down it. They have now made it 2 lanes half way down with a solid white line stopping anyone overtaking and creating a head on situation. It then narrows to 1 lane and the traffic coming the other way have 2 live lanes.Just trying to find a road like the one described, that im pretty sure still exists. Its been about 4 years since i went that way though say may not do.
Found it, the A4112 Between Leominster and Clyro (Hay on Wye)
Google Maps
The bit of the A4112 you are thinking of,is Dilwyn bypass. The A40 Oxford and Witney bypass used to be three lane,several drivers killed in the 60.s.
There was the “Mad Mile” between Tring and Aylesbury on the A 41. Serious amount of accidents there in the '60s.
A fair bit of the A4 was set out like that iirc, the stretches between Newbury - Hungerford - Beckhampton- Calne spring to mind .Road is still the same width but with only one lane each way with a “ghost island”(is that what they call it?- not chevron markings but something akin)running down the middle. 
There is a short section of the A494 (Mold to New Brighton) that is single carriageway with a central suicide lane up the middle. Doesn’t work too badly as its pretty straight for about a mile but I have seen some pretty hairy incidents there now and again.
I use one quite regularly when not working. A30 between Camborne and Hayle