From Roader's Digest: The SABRE Wiki
|From:||Abington, Lanarkshire (NS929246)|
|To:||Gretna, Dumfriesshire (NY331669)|
|Length:||48.5 miles (78.1 km)|
|Meets:||M74, M6, A702, A75|
|Route outline (key)|
The Abington Interchange is where the A74(M) and M74 change numbers, and also forms the main access to Edinburgh from the motorway network. It was formerly a fork junction between A74 and A73. During the motorway construction in the early 1990s, the junction was rebuilt into the present layout.
Crawford & Elvanfoot Interchanges
The Crawford & Elvanfoot Interchanges are a series of junctions all belonging to J14 of the A74(M). It best to think of this junction as one even though the distance between the Entry & Exit slip roads of the southbound A74(M) is 2.8 miles (4.5 km) apart. These set of junctions are very much like the Sawtry Interchange on the A1(M) and the Leatherhead Interchange on the M25.
Guards Mill Interchange
The Guards Mill Interchange is the southern terminus of the A74(M). It is a ½ diamond and it was built in the 1970s. Today it is where the A74(M) becomes M6.
These services are shared between the M74 & the A74(M) and are operated by Welcome Break.
Gretna Green services
These services are the last on the A74(M). These services also has a secret exit to the B7076.
See main article: M74 and A74(M) History.
Since the 1990s, the route between Glasgow and the border has caused confusion for changing numbers at Abington (J13). This was exacerbated in December 2008 when the M6 was extended to meet the A74(M) at Gretna, thereby filling in the Cumberland Gap. Given that the three numbers were three separate stretches of motorway when the first section of A74(M) opened, and that the A74(M) was a temporary number (in the traditional style of the A48(M), etc.) it was a fairly logical thing until the planned renumbering didn't happen when the gaps were filled.
In effect, the M6, A74(M) and M74 are now the designations given to three sections of a single continuous motorway, with two en route changes of designation (unintentionally at the border and the turn-off for Edinburgh). The southernmost and by far the longest section is the M6; the M74 is the northernmost and shortest, with the A74(M) in the middle.
Situations like this are common in France where, for instance, the A6 and A7 terminate end on in Lyon, with the A7 having been built from Marseilles and the A6 from Paris (other situations occur where toll motorways and free motorways have different numbers: eg. A71 and A75). However, the M74–A74(M) join is unique and the most bizarre.