Helmar

I'm wondering if anyone else has experience this safety issue with the Active Cruise Control system?

Normally, the ACC functions flawlessly, in all situations.

Problem Scenario:

1. Driving at around 35-50 with ACC engaged.

2. Approaching cars stopped at a stop light. The road approach is slightly uphill until around 100 feet before the stopped cars, at which point the road levels out.

3. The ACC never "SEE"'s the cars, as is evidenced by the lack of the small car icon in the ACC section of the speedometer, and the fact that the car continues at the same speed.

4. I let the car have it's head, and even after I've passed the hill portion and am on level ground, with the stopped cars around 100 feet ahead (and lessening as I approach), the ACC hasn't "seen" the stopped cars and continues speeding along, without the icon in the speedometer indicating that it has seen the cars.

5. Finally, when my nerve gives out, I strongly apply the brakes.

I've tried this about a dozen times, with identical results.

Anyone else hear of this issue?

HBH

irenesbob

I do not have ACC but the situation you describe does not surprise me. Such devices need to have a learning or memory function (as you do) so that once it comes upon such a situation, the GPS will tell ACC to get ready to brake ahead if needed. The human mind is incredible, we do stuff like that all the time.
Auto pilot and such work on airplanes (at a huge per installation price tag) but also depend on a control tower monitoring radar and sight events as backup. I feel there is a lot of further development needed before I would trust this kind of system when I am driving. side Assist and other passive aids are good, but this kind of stuff is a bit scary. When I had my recent deer hit (car is still in the shop 28 days later) I was wondering what (if anything) ACC would do when and if the speeding deer came into its peripheral view. Probably nothing.

Helmar

Thanks for your reply, but it would seem to me that a radar system would either see or not see a stationary object ahead, without any training.

It's obviously not seeing it, as the "small car icon" in the ACC display is off.

I'm a software developer, and this smells like a software bug to me...............

I'll be bringing my car in for it's 15,000 mile servicing in about a month and will ask them about it.

HBH

DeerHunter

ACC won't "see" stopped objects (including cars), unless they were originally moving while in its field-of-view. What you describe is completely normal.

Helmar

ACC does indeed see stopped objects, except for the hill.

Every other time I approach stopped cars while the ACC is engaged, and there's no hill preceding it, the ACC sees the stopped cars and behaves appropriately....

Yours doesn't do this?

HBH

joebird

There's an example in the User Guide (which I don't have in front of me) where a moving car (in front of your car) changes lanes, and if there's a parked car behind that the system won't work correctly (isn't expected to in that situation apparently).

This may infer that the auto-brake feature relies more heavily on the camera in the rear-view mirror which can detect movement than on the radar sensors in the bumper which I assume detect range. Just a guess though -- pure speculation.

Xtek

I believe it actually states in the manual that the ACC does not track stationary objects.

DeerHunter

No, my car behaves as expected.

To clarify: If you are following a moving vehicle (within range of the sensors) and it slows to a stop, then ACC will make note of that now-stationary object and stop your car. If you crest a hill (or, as joebird notes, the car ahead of you switches lanes) and a stopped vehicle presents itself, then ACC will not make note of this and will happily plow right into it.

Bottom line: ACC is a useful assist in stop 'n go driving, but you still have to pay attention and be ready to drive the car.

superswiss

Correct. ACC and PreSense (specifically Brake Guard) do not detect stationary objects. Audi has not yet introduced a system like Volvo that detects stationary objects and brings the car to a full stop without driver intervention. Audi's implementation is an assist feature, but ultimately the driver needs to pay attention. PreSense and Brake Guard help along with features such as jolting the brakes to get the driver's attention, pre-load the brakes, pre-brake up to 30%, but none of these features react to stationary objects. It will detect stationary objects if they were moving at the time they came in range of the system. If it feels like it sometimes reacts to stationary objects it simply had tracked them already without the drivers knowledge. The system tracks moving objects ahead whether they are currently in your lane or not, long before the green car symbol displays in the dash. The green car symbol indicates that it is actively following a specific car ahead, not that there is a car in range.

superswiss

The system tracks moving objects ahead of you long before you know it. It tracks them in your current lane as well as in neighboring lanes to see if any of them are moving into your path or you are moving into their path. The green car symbol in the dash does not indicate that it detected an object in range. It indicates that it is actively following an object ahead of you. If it feels like it reacted to a stationary object, it simply means that it was tracking the object already while it was moving and you simply didn't know.