Is runng over a bird with your car bad or good luck?

Not all naturally occurring phenomenon can or should be interpreted as a sign or omen. In this case it is most likely just a simple interaction between nature and technology that had unlucky results for the bird. There are any number of birds that frequent the sides of roads, the law of averages says that when they fly up, a certain percentage will choose a path that will have fatal results.

If the bird was of personal significance to you, then you may want to look closer into the incident, but in that case it is essential that you know the breed of bird.