ANPR probably wouldn't work on the many foreign vehicles which use the A205, and they may not understand that the flashing sign refers to them (with their sometimes limited English), so TfL is right that some drivers may not notice the warnings until they see the bridge.

However, once the truck has turned onto Waldram Place, it'll have a hell of a problem getting onto Perry Vale, so it would probably cause delays and difficulties on the network anyway, which makes their argument void.

Perryman - Overheight vehicles approaching from the west are indeed directed down Devonshire Road