Interesting ACC/FCW interaction
Yesterday's commute had a bit more challenging than usual, and ended up having the FCW go off 4 separate times. One mildly interesting thing is that all 4 times were with the ACC on. Also note that all of them were due to traffic slowing down in front of me (i.e., no cross-traffic, turns, etc.). Since the FCW is supposed to trigger if it thinks a crash is imminent without further actions, I'm a little surprised it would trigger with ACC on, especially since the ACC seemed to be braking appropriately for each of the situations. I suppose I could understand them wanting to warn you with these sudden changes so that you're prepared to take over and don't rely exclusively on the ACC. But I still find it interesting.
The more interesting one was when I decided to actually take over and touch the brake. In my opinion, the ACC was braking appropriately for the situation, but I decided to touch the brake anyway. As soon as I touched the brake, it started braking even harder than what the ACC was doing, more than I was doing, and more than I thought was necessary.
So for the most part the FCW was acting the way it's described. With the audio/visual notification going, if you start to brake and it feels the braking is insufficient, it will increase the braking. The thing I find curious though is that it seems that the FCW is more "conservative" than the ACC.
Now I do have the FCW set to Far and I have the ACC set to "3 bars" (e.g., 1 bar less than its most conservative setting). So there is potentially a slight difference in the conservative settings. But given that the ACC should maintain a safe following distance, and FCW is trying to mitigate a crash, you'd think the ACC braking would be more conservative.
It also seemed to me that the FCW was more conservative at lower speeds than at higher speeds (somewhat paradoxically). There were a couple times when I was traveling at about 70 and traffic slowed rather suddenly, but I let the ACC do its thing and it braked pretty darned hard (and caused me to have my foot hovering right over the brake because I was starting to get a little "pucker factor") but the FCW never went off. Yet in the other instances, where the FCW did trigger (still while ACC was on), I was traveling between 30-50mph and the ACC braking was not as hard (nor was the pucker factor as high) as the instances at higher speed. Very unscientific and very objective, I know - but that was my perception.
Anyway, still absolutely LOVING the ACC - I can travel almost my entire 50 mile-each-way commute without ever touching the gas or brake. And I'm still leaving the FCW set on far. Just found the behavior a little perplexing in some of the situations.