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: A421 ; Bedford; M. Keynes (S).
Forward destinations: London, Dunstable, Luton M1.
Junction number: 13.
We'll get our third lane back at the other side of junction 13, but enough traffic leaves here to call for the left-hand lane to temporarily depart.