M4 westbound traffic wishing to access the A34 is advised to exit at junction 12 and travel west along the A4; and M4 eastbound traffic wishing to access the A34 is advised to exit and junction 14 and travel east along the A4.
Junction 8/9 near Maidenhead, Berkshire, and High Wycombe, Buckinghamshire is the only one in the UK with dual numbers. This arose at the time when the M4 turned north near junction 8, where it met the A308, and headed for the original junction 9, where the motorway ended at a roundabout interchange with the A4.