My $20k Mazda won't allow me to rear-end somebody even if cruise control is switched off. Neither will my wife Subaru.
I'm pretty sure my Subaru does the same. But I'm not brave enough to actually try a rear-end.
I've been thinking of getting a big cardboard box to try with, but so far it's only an idea :)
Civic 2016
When these systems were new, many vehicles were only able to decrease collision speeds. These days, many vehicles completely avoid crashes at both 12 and 25mph.
Even a new base Honda Civic won’t hit the car in front of it at 25mph. (Or a pedestrian!). https://www.iihs.org/ratings/vehicle/honda/civic-4-door-hatc...
FWIW, Then unintentionally I had a bit of real world confirmation: a few months ago a car in front of me in slow traffic made a very sudden and complete stop.
I stepped on the brakes; after a second, as I slowed down, the brake feel completely changed and became harder, and I realized that I hadn't been alone - initially, car was braking for/with me, as confirmed with the massive orange letters on the dash board. Then as the system felt it was out of most immediate danger, it released and it was just me braking (that was the brake pedal feel change).
I do occasionally have it engage stage 1 of 3 (1 Visual -> 2 Audio -> 3 Auto Brake). It happens once a month predictable on very slight curves when it thinks I may be accelerating into oncoming traffic.