After making a precautionary landing on a two-lane highway and adding oil to the airplane’s engine, the pilot attempted to take off from the highway. The local police provided vehicle traffic control and blocked off the amount of highway the pilot estimated that he would need for the takeoff. According to the pilot’s report, he was reaching takeoff speed when he realized that he would not be airborne in time to clear a police vehicle. He altered his takeoff ground roll to the right in an attempt to avoid the vehicle. The right wing of the airplane impacted a highway sign, and the airplane continued off the highway to the right and down an embankment. It nosed over and came to rest inverted, resulting in structural damage to the wings and the vertical stabilizer. The pilot reported that there were no mechanical anomalies with the airplane or its engine during the takeoff attempt.