Hi. Safe following distance is the distance required to safely stop at whatever speed you are going. At a typical speed of 90km/hr (that's usually when this "feature" gets engaged - slowing me to 10km/hr under the limit because that's what someone in front of me is doing), the safe stopping distance is around 80-90 meters (perception+braking in good conditions). The shortest follow distance setting I seemed able to find was around double this distance.
tl;dr: I do not find that the adaptive cruise control is engaged at a safe following distance. Indeed, I think it makes me less safe as a driver, because it slows me down arbitrarily without any visual or auditory notification.
The LONGEST following distance maintained by Toyota's adaptive cruise control is 50m (at 80 km/h). The short and medium settings are 30m and 40m.
So either (a) the car you drove was defective or (b) you are radically misjudging your following distance. I know you are inclined to assume the former, but keep in mind that humans are terrible at judging distances when moving at high speeds, and most people leave way too little space between them and the car in front of them.
I make a habit of counting seconds between cars (particularly in light traffic, which is also the only time I'm using cruise control), aiming for the standard 5s follow. At 90km/hr (25m/s), you're telling me Toyota's cruise control has a maximum follow distance of 2 seconds? That is incorrect from my experience (and unsafe from standard driving practice). Where did you get that number?
I looked it up in the owners manual for the Toyota Corolla available online.
(While I haven't driven a Toyota Corolla with adaptive cruise control, I have driven a Subaru Forester, which uses roughly the same following distance; I find it to be a little closer than I'd prefer on my own, but accept it for the convenience and because I assume it can get away with a shorter following distance, since it is not reliant on human reflexes to stop in an emergency.)
You are not going to get to your destination faster by staying closer to the car in front of you. You'll still be restricted to 90 minus 10 km/h.
Not that this is even a problem in the fist place, I've used dozens of cars with ACC, no Toyota in particular though, and all of them allow adjusting within almost armreach close to a long 5sec gap. Put closer distance in heavy traffic to prevent lane jumping in front of you and 5 sec for comfortable highway cruising.
Most of my cruise control driving is on very low traffic volume divided highways. With regular cruise control, if the distance to a car gets smaller, I know there is a speed differential and I can slow down or pass, as appropriate. With the adaptive cruise control, the system as decided for me that slowing down is the correct option, generally before I've gotten close to where I would normally pull out to pass. With the long follow distance and the very gentle deceleration, I generally don't realize the system has slowed me down. This would be good as long as slowing down is the decision I want, but my cruise is generally set at the speed limit and I'm slowed by someone driving slower when the conditions don't warrant.
