As everyone else has said, the NYC subway is very safe pretty much round the clock. That being said, the cops I've worked with (including a number of former transit cops) recommend starting to be a bit more careful after midnight or so. read more
Late Night Tips. The subway is generally safe most hours, however it can become unsafe in the late hours of the night or wee hours of the morning when usage drops off. Still, riding the subway alone at 3 am without being harmed is possible. read more
Jan 19, 2013, 1: 54 PM subways are as safe as any form of transport at night. just be aware, as much as you would be on the street. the most prevalent crime is petty theft from sleeping or distracted passengers. read more