When starting from a full stop and traveling approximately 25 mph, a car crosses in front of me. I make an emergency stop to avoid a collision. The car will then not shift out of first gear. I then must safely get off the highway, stop the car and when I restart the car everything works fine. This has occurred three times under almost the exact scenario over the first year of operation. This problem provides an unsafe condition for the caras occupants as well as others on the road. I have had the car inspected by three separate Porsche dealers. Their position is that they can find no problem with the car, but have never tried to reproduce the event (to dangerous). I have volumes of reports from Porsche, all saying that they can find no problem with the car .