The A601(M) is a short link road that connects M6 junction 35 to the local road network just north of Carnforth. It's just a mile of nondescript dual carriageway, but is one of the UK's earliest motorways and has a surprisingly complex history.
The motorway started life as part of the M6 itself, and for ten years formed the northern terminus of the Lancaster bypass, which opened in 1960. The northern end of the M6, until 1970, was here: the motorway turned a sharp corner at what is now junction 35 and ended at the roundabout with the A6 at modern-day J35A. When the M6 was extended northwards, it branched off at a new junction, leaving behind a spur to the A6. For the next 17 years this was just a simple motorway spur from the M6 to the A6 and didn't have its own number.
One of the main uses of junction 35 was for traffic accessing the M6 from a quarry at Over Kellet, just south-east of the spur, and all those heavy loads had to pass through Carnforth to reach the motorway. That was evidently silly, when the journey passed right by the motorway junction but couldn't access it without taking a long route through a town centre. So, in 1987, the Over Kellet Link opened, an extension of the motorway spur eastwards from M6 junction 35, running the short distance of two hundred yards to reach the B6254.
The extension connected only to motorways so it was placed under motorway regulations too, but it's a single carriageway road, with one lane in each direction. The result was a motorway from the A6 to the B6254 that stopped halfway along to negotiate a roundabout, was partly single carriageway, and ended on a B-road at a Give Way sign. It was one of the very few single carriageway motorways in the UK - the others are a short link from the end of the M58 to the A577; an unnumbered connection from the M61 and M65 to Walton Summit; and the former A6144(M), which was downgraded to an A-road in 2006.
As if this didn't make the road strange enough, somebody at the Department of Transport decided that the spur extending in both directions from the M6 made it eligible to be given a route number of its own. For reasons that have never been properly explained, they called it the A601(M), a decision that makes no sense whatsoever. "A601(M)" ought to be a part of the A601 under motorway restrictions, or a motorway bypass of part of the A601. But it's neither, and if you look at a map of the area surrounding Carnforth, the A601 is nowhere to be seen. In fact it's a very long way away: the A601 forms part of the Derby Inner Ring Road, more than a hundred miles to the south east.
In early 2020, the single carriageway link towards Over Kellet was downgraded and lost its motorway regulations, as did the roundabout at junction 35, so that Lancashire County Council could grant planning permission for an access from the link road to new commercial developments near the motorway. The link road and roundabout were given the number B6601, which has had the effect of disconnecting the A601(M) from the motorway network. It is now a dual carriageway between two roundabouts with an inexplicable number and a connection to the M6 that is made, technically, by travelling on a B-road.
Between its prestigious history, its strange layout and its inexplicable number, the A601(M) can keep a road enthusiast busy all day - which is more than can be said for a driver. At just over one mile in length, the whole road can be negotiated by a determined motorist in about one minute.