In short, it depends.
"Huh?" you ask.
Although police can, on occasion, be held to the same negligence principles that govern the rest of society, there are instances where they will be immunized against liability for a auto accident - i.e., if they were in the process of responding to an emergency, and were not driving recklessly under the circumstances. Under the emergency doctrine, the police's actions are gauged by a recklessness standard rather than one of negligence, giving them far more protective cover.