That doesn't solve it at all, you're thinking of a different problem. I got clued in from another comment that only mentioned it offhand, but this is the problem the "Pittsburgh left" tries to solve:
The traffic is a single lane, and you want to turn left. Light turns green, and you wait for the oncoming traffic to clear. All traffic behind you is stopped on a green because they can't get around you.
Even with multiple lanes this can be an issue as people behind you try to merge right to pass you which in busy traffic increases the chance of accidents and causes slowdowns.
Indeed. When I first came to the US I lived in Boston and this happens quite frequently inside the I95. It used to drive me crazy, I hated it, I though it was dangerous and uncivilized :-) it didn’t take long for me to understand why it was necessary and to start doing it myself.
For a responsible driver, it is a test to see if you are paying attention. A careful driver will see this about to happen, anticipate it, and allow the turning driver to make his impatient left safely.
If single lane road deadlock is a problem, the city's urban planners should (and probably will) install a left turn signal to solve it. A better solution than reckless driving is to report the deadlock to the city.
Many of the roads in the city of Pittsburgh are carved into the mountain, sometimes with shops or houses on either side between the road and cliff face. The terrain there is not a trivial thing to engineer around.
You clearly have never been to Pittsburgh. There is simply no room at some intersections for a left turn lane, and a left turn signal would needlessly block traffic going the other way even when nobody wants to turn left.