Smart Motorway gantry sign
A gantry structure spanning the motorway with electronic signals, blue signs showing a "tiger tail lane drop" where the left lane exits, the right hand two lanes continue ahead and the second lane from the left can go in either direction, and the following text.
Exit destinations: M23 Brighton, Crawley; Gatwick [Airport symbol] Croydon .
Forward destinations: Reigate (A217), Watford & (M1); Heathrow [Airport symbol] (M4) M25 .
Junction number: 7.
Change Route: M23 Gatwick & Croydon
This is Merstham, one of the UK's three Four-Level Stack interchanges. As we get closer to the junction multiple levels of flyover come into view, and if you stay on the M25 you'll pass underneath the whole towering pile.