At 40 miles/hr in traffic, car started accelerating. I don't know how high the rpms went, but it sounded like it wanted to go airborne. I had to stand on the brakes, literally standing, with the butt out of the seat, just to keep it at 40. Pumped brakes. Messed with cruise control buttons. Finally on uphill dropped to 20, with engine still revving, pulled to shoulder and punched it into park. Didn't know I should have punched it into neutral. Car stopped by engine still continued to rev until smoke came from under hood. Then it stopped. Car was drive-able. But I'm not going to drive it again. This happened once before briefly a week prior but was over quickly. The second incident lasted hours - OK - maybe 5 minutes. But it sure felt like hours. I was scared to death!

Update from Feb 18, 2017: delete