In order to set a new Road Rule on Watt Street in Burnout Paradise you have to to beat the offline record for this street. Watt Street is located in the north-east corner of the map. Your goal is to drive through this street as fast as possible, so pick the fastest car you have, or some of the legendary cars.
Before you attempt the Watt Street Road Rule, press up on the d-pad until you see “Best Offline Time”. Now your time will be registered and you can complete the Watt? Achievement / Trophy.