| 1971 – present|
The A308(M) is a motorway in Berkshire, England. It is 0.6 miles (1 km) long. It runs from the M4 at junction 8/9 to the A308.
A308(M) motorway Wikipedia
In 1961 the A4(M) was opened and ran from the existing junction 7, through a junction with the A308 and ending at a junction with the A4. In 1963 the Slough bypass was opened to junction 7 and the A4(M) was renumbered M4, junction 8 being with the A308 and junction 9 with the A4.
The proposed route of the M4 was then changed to go south of Reading, instead of north of it. When the M4 was extended in 1971, a new junction was provided to connect with what would become a spur. This new interchange was built too close to the original junction 8, so this had to be closed. A new junction (numbered 8/9 so as not to confuse motorists) was built. The original M4 north of this was renumbered as the A423(M) and in the 1990s this was again reclassified as the A404(M). A new spur, the A308(M), was built to maintain access to the A308 and connected with the A404(M) and the M4 at the same grade separated roundabout.
Information above gathered from Advanced Direction Signs April 2011