4. Severn Railway Bridge, which crossed the Severn between Sharpness and Lydney.  Severed after being struck by river boats, and subsequently demolished.

There's a pleasant walk from Sharpness docks, which have a very deep lock from the tidal river, along the canal and past the base of the swing bridge that carried the railway over the canal.

Is the link that all the bridges fell down for one reason or another - how the mighty are fallen?

3.  Is Bennerley Viaduct near Ilkeston on the former GNR Nottingham (Victoria) to Derby (Friargate) line.  However the viaduct has recently been restored.   

1 is Meldon, which was, and is, in an industrial setting even if the industry is now mostly archeology. The viaduct's still there, but no one would dare to sign off sending a train across it. The new Dartmoor line will see a slim, economical, elegant concrete structure built, close alongside, rather nearer to the camera and on a faster alignment, here's a concept trace.

Mark