NYC subways have additional safety features - if the track signals indicate stop (due to imminent collision with another train, for example), there are tripcocks. These raise from the tracks, and catch on the bottom of the train, causing it to hard break immediately.
Failsafes don't always fail safely. Take the unmanned Chicago subway train that cruised through the failsafes and crashed into another train, two weeks ago. Another article quotes a CTA official as not knowing how it could have escaped the yard without the brakes tripping.
