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Britain has a long history, and has many ancient roads and trackways dating back to the Roman occupation and before. With the advent of the car and the huge expansion in the numbers and standards of roads, as well as the introduction of a national Highway Code, a coherent numbering scheme was developed, which is still in use today.

The road numbering system in England and Wales is based on a radial pattern centered on London. Scotland has an extension of the scheme based on Edinburgh.

## Main trunk routes in England

Main trunk routes from London have single digit numbers, starting with the A1 which heads due north. The numbering continues sequentially in a clockwise direction, thus:

## Main trunk routes in Scotland

Similarly, in Scotland, main trunk routes radiating from Edinburgh have single digit numbers, thus:

These radials are supplemented by two-digit codes which are routes that are slightly less important (but may still be classified as trunk routes). These routes are not all centred on London, but as far as possible follow the general principle that their number locates them radially clockwise from the associated single digit route. For example, the A10 (London to
Cambridge) is the first main route clockwise from the A1, the A11 (London to Norwich) is the next, and so forth. Some of the more important ones are:

The system continues to three and four digit numbers which further split and criss-cross the radials. Lower numbers originate closer to London than higher numbered ones. Knowing the number of the road you are on will give you a rough idea of where you are geographically once the system is understood. Some of the most important are:

"B" roads are routes which have lower traffic densities than "A" roads. The classification has nothing to do with the width or quality of the physical road. B roads follow the same numbering scheme as A roads, but almost always have 3- and 4- digit designations. Most 3-digit B-roads are former A-roads which have been downgraded due to new road construction.

## Motorways

Motorways came to Britain much later than the established routes and the numbering system was already in place.

Therefore the motorways are designated "M" roads and are numbered to match the existing main radials which the motorways in general follow. One exception is the M5 whose closest A-road equivalent is the A38. The numbering of two digit motorways is based on a zone system formed by the 1-digit motorways, not on the zone system formed by the 1-digit A-roads. The other exception is the M6 Toll a recently opened toll motorway which bypasses the busiest section of the M6 around Birmingham.