Smart Motorway gantry sign
A gantry structure spanning the motorway with electronic signals, blue signs showing an exit and the following text.
Exit destinations: A5183 St Albans (N).
Forward destinations: London, St Albans M1.
Junction number: 9.
The A5183 used to be the A5, and as originally built in the 1950s this junction provided fast free-flowing connections to and from the M1, since it was the crossing point of two trunk routes. But the M1 made the A5 largely redundant, and it's been re-engineered as a local junction.