Have had MS for several weeks now and overall really enjoying the car. Have had lots of very good experience with TACC and AP. Last weekend, was driving in stop and go traffic (up to about 40 mph and down to stop), when the TACC system did not slow down as we approached the car in front of us. The car ahead was slowing down rapidly, but it was not a sudden stop of the car ahead. I waited for the MS to brake/slow down, but it did not - until the collision warning sounded (so, good to know that works!) and I hit the brake, when we stopped very sharply and it got the attention of everyone in our car. I assume the system is designed to brake well before the emergency braking system starts to kick in (but good that they seem to be separate . . . ); this was a little scary. The car ahead did not swerve into the lane; i had the follow car length set at 4 car lengths. The only thing I had changed was I had just put an external transponder for EZ pass on the license plate - any chance that interfered with the TACC system? I had generally been watching to make sure that if there was a car ahead of me, it was showing up on the display screen - I assumed that meant that the car ahead was being tracked and the MS would respond as the gap closed. Any thoughts? I am a little bit less trusting of the system than I had been.