I'm in California. In our state, it's part of the Vehicle Code, but courts regularly construe it as applying anywhere in public. I have personal knowledge, unfortunately, that violating the California Vehicle Code is in many cases a criminal and not civil matter. The statute doesn't include any qualifier that the order be lawful. I suspect that "and was performing his duties" is meant to cover that question, representing a legal fiction that cops would never issue an unlawful order.
For those who are interested in reading beyond Galpern, some other relevant classic cases are Terry v. Ohio and People v. Cohen.