So I was driving today around 60mph on a 55 mph divided road (2 lanes going one way and 2 lanes going to the other way with a guard rail between the two) I had just TACC engaged. I was coming up to an intersection and the traffic light was red. There was a pick up truck in front of me and a huge semi truck in front of the pick up, already stopped at the red light. As I was approaching the red light, the pick up truck turns his right blinker on signaling that he was going to move over to the right turning lane to turn right at the intersection. This would suddenly leave just the stopped semi truck in front of me. I did not want to take the chance of TACC not stopping for the stopped semi so I cancelled TACC and slowed down manually. I know situations like this where a vehicle suddenly moves out of the lane to reveal a stopped vehicle in front of you can be tricky for TACC. Furthermore, I did not know if the underride guard on the semi would confuse the radar. I manually cancelled TACC because I feel it is better to be safe than sorry. It is important to remain vigilant when using TACC or AP. What do people think of this situation? Have you encountered the same situation and what does TACC do?