In message , Richard J.
writes
The Thames bridges also have "traffic lights" for vessels, so this
is actually a SPAD as well!

I doubt it. AFAIK the lights are to show which bridge arches are
available for navigation. There was no reason to stop vessels passing
under the bridge, but it's the skipper's job to ensure he has enough
headroom.

I still think there'd be *additional* signal lights to indicate when it
was lifted.

ps Lifting schedule:

http://www.towerbridge.org.uk/bridge_lifts_schedule.htm
--
Roland Perry