A real experienced driver can reverse a B-double into anywhere. The trailers don't lock. They are always double articulated.
If there was any problems, the driver could pull up near to where the dock was, and unload the trailers seperately, but it makes the drivers cranky if they have to do this. It just takes more time. And of course, to unload the front trailer from the rear, the back one would have to be dropped off anyway.
I'm not a B-double driver. I just load and unload a lot of them though.
See ya's.