Up at City Hall Plaza, the Big Apple Circus is in town, and they close off the parking lane as a fire lane during performances.
On the Longfellow Bridge, they're doing something to the railings and stone, so they are closing off the lane. When they first put it all in, the lane merge sign was put so that you couldn't get around it on the right, and had to go around a barrel, into traffic to get around it on the left. I emailed Mass Dot this picture, and they have since moved them so that you could get through pretty comfortably.
It's really nice to have that extra space!