Motorway cantilever sign
A blue overhead sign suspended over the motorway from a post on the left, with a diagonal arrow pointing up and left, and the following text.
A4 Slough (W).
Junction number: 7.
We're now on the oldest bit of the M4 - the Maidenhead Bypass opened in 1961 and the Slough Bypass in 1963. It was only two lanes wide back then, and has since been doubled in width.