Adaptive Cruise Control - a cautionary tale.

[AlanD]

The ACC got caught out yesterday

Travelling city bound along the Monash Freeway at 100 kph (the posted limit) and moving through a gentle right hand bend that required no steering input owing to the road camber.

Quite suddenly the car started an almost panic stop that washed off the speed quickly until I took back control of the throttle.

I'm suspecting that this occurred because there was an almost stationary vehicle on the left hand verge. I'd guess it was moving at between 10 and 20 kph waiting for a traffic gap to pull into.

Because of the bend the ACC beam washed across the slow moving vehicle and believed, since there was no steering input, that the car was running up behind another car in the same lane moving very slowly and commenced a rapid slowing manoeuvre. Thankfully the car behind was not tailgating so there was no collision but a quick glance in the RVM showed a rapid closure rate.

I've had similar situations on a straight road with no concern, so the ACC beam is quite directional and is able to differentiate stationary objects from moving ones. It can also detect cars that pull into the gap I leave to the car ahead and takes no action if they are moving faster than me. If they are moving slower then an adjustment occurs to maintain my preferred separation distance.

Some very clever calculations are being done by the system - but it isn't foolproof as my experience shows.

Cheers

[thebigd]

It's a great system, but not perfect, even though it's just doing it's job.
I've had similar issues to the one you report. It gets your attention pretty quickly, especially if someones close behind you, not expecting you to brake.
Have also learned to switch it off while climbing the Toowoomba Range, and Cunninghams Gap. There's a couple of sharp right handers on both crossings that activate the braking. There's been no cars around, so I guess it's picking up the terrain directly ahead, before you hook into the turn.

[NX74205]

I've had a similar experience, actually. But in my experience, I've found that it never behaves unpredictably. Whenever it slams on the brakes, it does so because either a car has just merged into the gap in front of me, or I'm going around a slight bend while passing a slow moving car.

These days when I'm in a situation where the ACC could potentially slam on the brakes, I deactivate it temporarily.

[Martyvan]

Originally Posted by NX74205

These days when I'm in a situation where the ACC could potentially slam on the brakes, I deactivate it temporarily.

If i can generally forsee the situation coming, and when its about to happen I turn a little towards it in my lane, and then steering input slightly away from it makes it all good.... not foolproof, and not all lanes support it.... but it kinda works in moat circumstances.

[sleek7]

Had the same thing happen many times in our MB Xr5t and in my PX2 Ranger. You learn to anticipate when it might happen with experience and I usually cancel the cruise when I suspect it might trigger. But would definitely scare the hell out of my 17yo sister in law who is still learning to drive.