Motorway gantry sign
A gantry spanning the motorway with blue overhead signs showing the following text.
Forward destinations: London, Bristol [Hollow circle diversion symbol] M4 .
Exit destinations: M48 Cas-gwent; Chepstow & Gwasanaethau; Services .
Junction number: 23.
Change Route: M48 Chepstow
Both M4 and M48 will get you across the Severn, meeting again on the far side, so you can pick whichever you like here. These signs are made up of rotating panels to show different messages if one or both bridges are closed.