I suppose he'll claim Judicial Immunity:
The accident happened just before 9 a.m. on what was to be a big day for the jurist: The nation’s highest court was hearing arguments in the massive Wal-Mart gender discrimination case. According to U.S. Park Police, Scalia was driving south on the parkway approaching Roosevelt Bridge when he rear-ended a car that had stopped for traffic, triggering a chain reaction.
Well, as Scalia has stated repeatedly and enthusiastically, there is no protection in the Constitution for rear-ending someone. So I say throw the book at the perp.