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: M40 ; London; (W & C) ; Uxbridge.
Forward destinations: Birmingham, Oxford M40; (M4, M3, M23); Heathrow [Airport symbol] Gatwick [Airport symbol] M25 .
Junction number: 16.
Junction 16 comes in two parts, thanks to the layout of its sliproads. This first exit, which takes away our left-hand lane, is just for the M40 towards London; in just a moment there'll be another exit on the left for the M40 towards Birmingham. Don't take the wrong one!