It was somewhat challenging to find good information online on crime at the PABT, but I found a few things that give some indication of how it has changed over time.
I would appreciate it if anyone can find better data or spot-check these numbers against other reports, because of course an order of magnitude is very large.
Between extrapolations from https://www.panynj.gov/corporate-information/pdf/10-board-me... and this New York Times article http://www.nytimes.com/1984/06/11/nyregion/as-port-authority... it seems that crime at the Port Authority Bus Terminal has decreased by a factor of ten from 1983 to 2013/2014. This seems to be consistent with everything else I have found on the subject, eg statistics in http://www.nytimes.com/1988/04/06/nyregion/bus-terminal-addi... which suggest an even greater reduction in robberies specifically.
I would appreciate it if anyone can find better data or spot-check these numbers against other reports, because of course an order of magnitude is very large.