Motorway lane allocation sign
A blue sign with a diagram showing the left lane exiting and two others continuing, and the following text.
Left lane destinations: (M11, M20); Stansted [Airport symbol]; Dartford; M25.
Right-hand two lanes destinations: (M40, M4, M3); Heathrow [Airport symbol]; M25.
Change Route: M25 Stansted or M25 Heathrow
By the time we branch off the M1, that single exiting lane has widened to a three-lane sliproad, and now it splits again.