Granted, this was about a decade ago, but I used to live in Quincy. I would say, Quincy is one of the safest cities in the metro area, and I used to take the red line home at hours like that all the time, and walked to my condo there. The red line to Quincy is safe. Just be sure to take the Braintree line, not the Ashmont one because it'll fork into 2 different directions right before it heads to Quincy/Braintree. It should say on the front or sides of the train which way it's heading.