yup that would be major pucker factor....
Heres a question on raised bridges and Tower Bridge in particular. Last summer wife and I took lunch break at Crab Shack Joe's in Old Town and had a good window seat in line with Tower Bridge.. During the hour we were there, the Bridge alarm triggered and raised three times.. We noticed the bridge could be manned since there's a cubicle on top. Conversation started with others in the restaurant.. Someone say's yea, its a manned bridge and boaters radio in requesting it to raise, another guy says you dial in with your marine radio and enter a special q-tone and someone else says no,, you need a special control box in your boat.. So i never have figured out what triggers Tower Bridge and other raised bridges in general... I bet you know 
Yes, it's manned 24 hrs. a day, just like all the other bridges. It's actually like a little studio office/apt. up there......desk, bed, restroom, heat and air, kitchenette, etc. and all the controls for the bridge, shipt to shore radio, back up radio, etc. They call the bridge with their ship to shore radio (marine radio), let the tender (bridge tender) know the height and length of their boat. Delta maps have the numbers for each of the bridges but they're also posted as you approach the bridges.