The police lights are on the whole time, I think once his headlights get broken by the deer, the lights are more noticeable.
Edit:
I was in a van with some other people and we hit a deer while I was asleep in the front seat. The last thing I remember is opening my eyes when I heard the noise just long enough to see the deer flying STRAIGHT UP in the air. Probably the funniest thing I've ever seen. I'm not sure how high it threw him but he got some nice hangtime.
Also, someone in front of me hit a deer a couple weeks ago and I couldn't avoid it and had to run it's head over.