The M58 is the motorway from north of Liverpool to Skelmersdale, Wigan and the M6. It's not all it was meant to be and in fact - like the M67 - it's one of those motorways that is unfinished at both ends.
In its unfinished state it provides a fast and remarkably quiet route across north west Lancashire, which has terrible junctions at either end, and indeed in the middle (in fact it has more CBRD Bad Junctions per mile than any other - one for every four miles of its route, on average), but provides three deserted lanes of flat, direct travel at almost any time of day.
To the east of the M6, a further section of M58 was planned to run across the south of Wigan to reach the M61, thereby providing another route between Liverpool (and its docks in Bootle) and Manchester. An underpass exists beneath the M61 just to the north of junction 5. The route was almost built in the early 2000s in a Wigan Borough Council plan for a local road called the A5225 - a watered-down road scheme that wouldn't quite have gone all the way to the M61.
There was also meant to be a much better onward connection from the west end of the M58 into central Liverpool, relieving the A59 towards the city. This never happened either, and without it the M58 stops in open land without really carrying traffic into the urban area at all.
Junction 2 is missing from the M58, for another never-finished idea. The M59 would have set off north from here, bypassing Preston to the west and ending on the M55, which is also missing its junction 2. It might seem that the M58 is a bit of an unfinished job - the truth is that it was cobbled out of other bits of road and it's something of a surprise that it exists at all. Much of the eastern half used to be the A506, built as part of the Skelmersdale New Town development and once called the Regional Road.
The M58 also has the distinction of being the only motorway to use a slang word (not an abbreviation) appear on its signs. "Skelmersdale" is referred to in one or two places as "Skem".