Since the burden of proof is on the government (U.S.), the police would speak first telling the story from its point of view. In due course, the defendant will tell his story. The defense would want to offer testimony that there was not a traffic violation when all the circumstances are considered. Example: a magistrate would or should consider that a motorist was speeding to take someone to the hospital. U.K and U.S. share common law principles and "reasonableness" is implied in law.
