Expunging your record is not going to do you a whole lot of good if you are applying for a law enforcement position. Many departments ask about all crimes committed, that includes crimes that have been expunged. As far as I know, LE agencies will have access to that information anyways, expunged or not. If you are going to tell the department that you are going to test with about the hit and run, I don't see a reason to get it expunged. They won't weigh it any less, even if it is expunged. Although expungment from your record is supposed to mean that it is erased from your record, it will never be totally gone. When your background investigator asks if you have ever committed a crime and you say no, you will be screwed, because they are not asking if you have a clean record, they are asking if you have ever committed a crime. My advice is simply don't lie about it.