Smart Motorway gantry sign
A gantry structure spanning the motorway with electronic signals, blue signs showing the left two lanes exiting and the other two continuing ahead, and the following text.
Left-hand two lanes destinations: M25 (M4, M1) Watford; Heathrow [Airport symbol]; (M20, M11) Dartford .
Right-hand two lanes destinations: London, Croydon M23.
Junction number: 8.
Change Route: M25 Heathrow & Dartford
The M23 progressively widens out on the approach to this junction until there are six lanes side by side - two for each of the directions on the M25 and two more for the M23. That's because virtually everyone leaves the motorway at this point.