At 225 miles (362km), the M6 is the UK's longest motorway and extends from Catthorpe (junction 19 on the M1) to the A7 North of Carlisle. From this junction (Junction 44) it joins a 6-mile (10km) section of A74 before becoming the A74(M) which itself joins the M74 to Glasgow. There are proposals to upgrade this "missing link" (there being a possible start date in March 2005), after which the A74(M) and M74 may be renumbered as M6, making it more than 360 miles in length.

The first section was opened in December 1958 (Preston By-pass) and the last in May 1972 (Bescott to Great Barr). It is generally dual three-lane carriageways, with short sections of dual four-lane between the M56 and M62 and between the M61 and M55. The section North of Birmingham is so seriously congested, that a new motorway, the M6 Toll, Birmingham Northern Relief Road opened in December 2003 to provide an alternative route.

There are a number of motorways which are 1 mile (1.6 km) or less in length. There have been conflicting claims on this subject, but it now appears that the A635(M), which is joined to the A57(M), Mancunian Way, is the shortest at about 300 metres long.

There are sections of motorway where local widening occurs to accommodate slip roads, and at these points, the motorways could well be five or even six lanes wide. However, the foreshore section of the M2 in Belfast, opened in May 1972, has a long section which is dual 5 lanes wide. More recently, opening in December 2005, the M25, between junctions 12 and 14, was widened to dual 5-lanes and the section between junctions 14 and 15 to dual 6-lanes.

The M62 is the highest motorway in the UK, reaching 1,220 feet (372m) AOD near to the boundary between Lancashire and Yorkshire close to the Pennine Way footbridge. The M6, passing over Shap, in Cumbria, reaches 1,040 feet (317m) AOD and is probably the second highest motorway, although the M74 at Beattock is thought to be at a very similar height. (AOD="Above Ordnance Datum", ostensibly sea-level)

The Alconbury to Peterborough section of A1(M) runs generally on the line of the old Ermine Street Roman Road, and is therefore "straight" for a considerable part of its length. Between Alconbury and Stilton, it is more or less straight for a distance of nearly 7 miles. Minor deviations have, however, been necessary near to Sawtry and Connington to accommodate junctions and side road diversions.

Design standards for motorways (and their intersections) require that gradients should be no steeper than 4% (1 in 25) except that in exceptional circumstances, gradients of 5% may be used over short lengths. Between the Shore Road and Sandyknowes section of the M2 in Northern Ireland, the gradient reputedly reaches 1 in 19½ (5.13%) in places. Shortly before the contract was let it was decided that a crawler lane should be added on this outward carriageway.

Steep gradients are often found on complex interchanges, but where the M90 terminates at the Craigend interchange with the southern by-pass to Perth, the topography dictates gradients said to be well above the recommended maxima. The actual gradients achieved are not yet known.

The longest section of motorway between junctions occurs on the M11. The distance between junction 8 and junction 9 is 15.2 miles (24.3 km). However, junction 9 only has northbound slip roads, and in a southbound direction there is an interrupted length of 17 miles (27.1 km) between junction 10 and junction 8.

The first to be opened was the Watford Gap Service area on the same day as the M1 - 2nd November 1959. It was operated by Blue Boar, but did not offer full catering facilities until September 1960.

The second M1 Service area, at Newport Pagnell, opened in August 1960 and was operated by Motorway Services Ltd.

In 1963, a further five Service areas were opened, Keele, Charnock Richard and Knutsford (all on the M6), Farthing Corner (M2) and Strensham (M5).