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: A4 [Hollow square diversion symbol] ; Reading (W); Theale.
Forward destinations: SOUTH WALES; Bristol, Newbury M4 .
Junction number: 12.
The M4 shadows the A4 all the way from London to Bristol, but this is the last time we'll meet it. From here it remains south of the motorway, out of sight, and we will make our own way west without it.