The numbering zones for A & B roads in Great Britain
In Great Britain, roads are given a letter with 1–4 numbers after it. This is how they are named. The letter is the category of the road. There are two main types of categories: motorways (with the letter M) and non-motorways. There are two types of non-motorways: A roads (with the letter A) and B roads (with the letter B). A roads are more important than B roads. There are also a very small number of C roads.
This system only applies to the island of Great Britain. Northern Ireland and other islands have their own systems.
In England and Wales, the six A roads with one number are most important roads coming out of London. Starting with the A1 which goes north, numbers go clockwise around London:[1]
A2 – London to Dover (the southern part of Watling Street, also known as the Dover Road; though the A2 past Rochester has been replaced by the M2)
A3 – London to Portsmouth (also known as the Portsmouth Road)
A4 – London to Avonmouth (also known as the Great West Road or the Bath Road; though this route is not used anymore to travel far since the M4 was built)
A5 – London to Holyhead (the Northern part of Watling Street)
A6 – Luton to Carlisle (the A6 first started in Barnet on the old A1)
In Scotland, important roads from Edinburgh have A roads with one number:
