This is a much more subtle maneuver than making a left turn in LA
for one primary reason: sometimes, you can make a left turn at the very start
of a green light, even if the opposing traffic has right of way.
It is very tricky to figure out when and where you can do this, because it is mostly at the whim of the driver(s) that DOES have the right-of-way at the start of the green light. What happens is this:
As the left-turn-making driver, you have to be very specific about how you approach the intersection. If you wish to make the Pittsburgh Left, you indicate this by inching slowly out into the intersection during the red light so that you are almost 1/3 of the way through the turn by the time the light turns green. The opposing driver, for his part, can concede the left turn by remaining still, or can indicate that he doesn't yield right-of-way by slowing making his way into the middle of the intersection during the red light. If the two drivers don't settle this during the red light (i.e. they remain either stubborn or indecisive over who gets/concedes right of way), then the real decision is made at the moment of the green light: if the driver with right-of-way stays perfectly still, then the left turn is conceded -- but if he doesn't wish to concede, then he must indicate this by accelerating rapidly and loudly into the intersection.
This may sound like nothing more than subtle automotive penis fencing -- which it is, certainly. But for the most part, people are very friendly about giving away the left turn, as there are many clogged one lane streets in the city. I have even had people wave me on even though I had remained stopped throughout the red light and initial moments of the green light -- essentially conceding the left turn without my asking for it.
If you are new to the city (and even if you aren't), I recommend that you never, never, never take the Pittsburgh left, even when it is conceded to you. Why? Because it is against the law -- and if God Forbid you should get into an accident while making the Pittsburgh Left, it will be entirely your fault in the eyes of the law. No matter what sort of signals (flashing high beams, waving, honking) are being sent across the intersection, the blame for any accident is determined strictly by the traffic laws. If while attempting a left turn you should misinterpret the cryptic automotive semaphore, then it is your tough shit to deal with.