I pulled into my driveway, came to a stop and planned to back up a short distance to be nearer the front walkway. Before I could shift into reverse the car started to accelerate forward. I slammed my foot onto the brakes which had no effect on the acceleration. The car stopped when the lower bumper hit and ran up onto a large boulder on the edge of the driveway. The car was partially wedged on the top of the boulder but I was able to back it off the boulder, park and turn off the car. I have scheduled an appointment with the service department on February 1st, at the dealership where I purchased the vehicle in June 2020. Of note, I had a routine oil change and service check at this dealership on January 16 with no engine problems noted.