Near where we live was one of the oddest stretches of motorway in the UK. It was only about 1.5 miles long but had a number of unusual features.
The A601(M) was originally the final part of the original M6 which ended just north of Carnforth. Opened in 1960, it was the third oldest section of motorway in the country. When the M6 was extended further north 10 years later, a 'spur' was left behind and this became the A601(M).
A few years later, a second shorter, narrower spur of the A601(M) was built on the opposite side of the M6, to give quarry traffic quicker access to the M6.
So the A601(M) was never exactly planned and has a couple of oddities.
First, the eastern spur was the UK's first stretch of single carriageway motorway, having just a single lane in each direction, with a double white line and a 70mph speed limit. This was the case until a couple of years ago when it was declassified and is now simply the B6601.
The second oddity is that when the road was numbered, there was already another A601, in Derby. No-one seems to know why the road number was repeated but it just seems to have been a mistake.
A couple of months ago, the main spur was also declassified and is now the A6070, a simple dual carriageway. Declassification means it can now be maintained to a lower standard, saving money for Lancashire County Council.
The truth is that it probably should have been declassified in 1970 when the M6 northwards was completed. So it got over 50 years of additional motorway life.