I was at the post office on Redwood Road in South Jordan, in the dropoff mailbox lane. At the end of the lane is stop sign. The stop sign is for the traffic coming into and leaving the post office. I was sitting at the stop sign when I turned east towards Redwood Road, as I was pulling up behind a blue SUV, the Frontier lurched forward and the RPMâs revâd all the way up and the truck shot forward. I put my foot on the brake trying to stop the car but it hit the blue suv at the stop sign, that was waiting to turn onto Redwood Road, and proceeded forward at what felt like a high speed into a blue sedan turning into the post-office. With the second impact the airbags exploded and the Frontier continued east bound across the remaining lanes of north/south traffic heading towards a house across from the post office. I had both feet on the brake trying to stop the Frontier, and in the end the only thing I could think to do is put it into park, so I grabbed the shifter and slammed it into park, effectively stopping the Frontier from plowing into the house. Guideline answers: 1. I experienced Sudden Unintended Acceleration, not sure what the failure is, except the brakes would not work and the vehicle would not stop. 2. Since I wouldn't stop, I hit two vehicles, and a man broke his sternum. Somebody, including myself could have been seriously injured or worse killed. 3. No, I can't get anyone to inspect the black box! I have tried many, many, times!!! 4. No warning