Needless to say there is definately a interesting legal side to photography these days and ones rights.
From what I can tell "photographing bridges" is perfectly legal from public land. It kinda falls into a grey area since some of them are owned/operated by private autorities that restrict photographs while on them and some stupid law saying pedestrians and motorists have to abay all signs posted on the bridges etc. So it seems to me that if you had your bigma out - handheld (as some places don't allow tripods on streets) you could snap away at anything you could normally see.
Of course I doubt many of us would risk the stress of dealing with police / possible false detainment / and destruction of camera equipment for our fun passion for photography. Also, I doubt any of us wants to, or has the time & money to go after a city on a contintutional/civil rights law suit. I imagine there are vulture law firms already preparing their case to sue the city/port authority and just waiting for the right person/situation to arise. I would not be suprised.
Its really sad what it has come to now.
Just be careful out there.
heres an interesting article about a few incidents - one being NYC bridges (its a bit dated)
PhotoAttorney has tons of articles and blogs on this type of stuff with some legal insight.