Smart Motorway gantry sign
A gantry structure spanning the motorway with electronic signals, blue signs showing the left two lanes exiting and the other three continuing ahead, and the following text.
Left-hand two lanes destinations: M25 (M3), Gatwick [Airport symbol]; Heathrow [Airport symbol]; (T4, T5 & Cargo) ; Watford (M1), Oxford (M40) .
Right-hand three lanes destinations: The WEST, Reading, Slough M4.
Junction number: 4B.
Change Route: M25 Gatwick & Watford
Junction 4B was added in between junctions 4 and 5 in the 1980s, and couldn't be called 4A because that already exists at the end of the Heathrow spur. It's your opportunity to forgo the temptations of The WEST in favour of the endless delights of the M25.