A-road gantry sign
A gantry structure spanning the road with overhead green signs showing the left lane exiting and the other two lanes continuing ahead, and the following text.
Left lane destinations: N and S Circular; (A406, A205); A4.
Right-hand two lanes destinations: The WEST; Heathrow [Airport symbol]; Staines, Hounslow M4 [Motorway symbol] .
Junction number: 1.
The A4 Cromwell Road rises up on its approach to the Chiswick Flyover, and two lanes of M4 lie ahead of us. There's no traditional "start of motorway" sign here - instead the motorway symbol on the gantry tells you we're joining a blue line.