Motorway fork sign
A blue sign with a diagram showing a branch off the road ahead and the following text.
Forward destinations: London; Bristol.
Exit destinations: Cas-gwent; Chepstow; A466; (A48) [Hollow diamond diversion symbol].
Junction number: 2.
When the weather is bad, all traffic can be diverted off the motorway here, so that high-sided lorries can be filtered out and only cars allowed to continue onto the Severn Bridge.