Factual error: Phil departs from the office right after the 5pm news. Punxsutawney is over 90 minutes' drive from Pittsburgh. The sunset in Punxsutawney in early February is about 5.30pm, so by the time they get there it should be completely dark. But it's bright daylight, without even a hint of twilight. (00:05:45)
Factual error: The train in the joyride scene is a Burlington Northern locomotive, which would never be found in Pennsylvania.
Answer: We know the police car survived because unit 2 is the car that followed them onto the tracks, and unit 2 is also one of the cars present when they are stopped (though it came from the wrong direction). The movie doesn't explain how the car survived so it is left to the viewer's imagination.
jimba