Being a new Model S owner, I am still familiarizing myself with everything, and have been using TACC whenever possible. This works well for traffic that is moving at a fairly constant rate, or is stop-and-go. However on two separate occasions, I have had to do a hard panic stop to avoid running into the back of a stopped car. Here is the scenario: I am going along fine using TACC, and the MS stays behind the next car well - that is, it keeps the distance I have set, slows down (and stops) when the car in front of me stops, and speeds up appropriately. However - after I have followed another car (which moved to another lane), the MS now speeds up to the set cruising speed. Going 55 mph, now I approach a car stopped in my lane (at traffic signal). The MS does not slow down at all, and I have to jam on the brakes to avoid rear-ending the stopped car. Is this normal behavior? (i.e., I am supposed to manage stopping for stopped vehicles myself, and not depend on TACC to do it) Is there something wrong with the way my car is working, or have I done something wrong? By way of background, Autopilot was disengaged during this; weather has been clear and it is daytime. The main reason I thought TACC should be able to handle this situation, was that when I did my test drive in Atlanta, I was directed to try using TACC in traffic, and it stopped like it should. Can someone explain?