Motorway gantry sign
A gantry spanning the motorway with blue overhead signs indicating one lane exiting, two lanes exiting in a different direction, and three continuing ahead, and the following text.
Left lane destinations: M4 The WEST; Reading; Slough .
Second and third lanes from left destinations: London (W & C); Heathrow [Airport symbol]; (Terminals 1, 2, 3) M4 .
Right-hand three lanes destinations: (M40, M1, M11); Oxford, Watford, Stansted [Airport symbol] M25 .
Junction number: 15.
This is Thorney Interchange, a Four-Level Stack built around a railway line, which passes through the middle in between some of the sliproads. Use it to turn left if you're bound for South Wales, or hang a right for one of the most direct routes to Central London.