Smart Motorway gantry sign
A gantry structure spanning the motorway with electronic signals, blue signs showing the left lane exiting and three others continuing ahead, and the following text.
Exit destinations: A355 ; Slough (C); (A332) [Hollow square diversion symbol] ; Windsor.
Forward destinations: SOUTH WALES; Reading, Slough (W) M4 .
Junction number: 6.
We're on the Slough Bypass, opened in 1963 as a very early two-lane motorway. It's been doubled in width since, with most of its bridges rebuilt to accommodate the extra lanes.