Has anyone worked out the ACC algorithm?

[Timothy Nathan]

Having now done a few long trips with autopilot (ie ACC and Lane Assist) engaged, I am now trying to work out exactly what is going through the ACC's "mind".

In some ways it seems amazingly capable, in others annoyingly stupid.


How does it know what the "target" is as you go round a bend? Say you are in the middle lane, with a stream of traffic in Lane 1, following a car. As the road bends to the right, how does it "know" to remain locked on the car, now off to the right, and not slow to the speed of the traffic in Lane 1 (now ahead of you)?
It seems to refuse to overtake on the left, but if you are on the exit lane (say M40 eastbound leaving for M25) and someone is doing 45 in a Moggie on the leftmost straight on lane, it drops the anchors, unless you anticipate with throttle.
Sometimes it jams on the anchors when there is a perfectly innocent car in the left lane, nowhere near in front of you. That tends to be on four lane single carriageway roads. Any ideas?
if a vehicle crosses your path dangerously close (turning right at lights against your straight on, for example) it seems not to take any notice at all and hurtles on regardless. Is that because there is no relative fore and aft movement?
Which brings me to the last point. If you are approaching the back of a traffic jam, such that the rearmost vehicle is stationary when you first see it, will the ACC stop? I haven't dared try!

[gbjk]

Timothy,

Glad you're having fun with the temp car! Suggest you try (4) in *their* car before yours arrives! ;)

1. Probably GPS/sat nav getting involved. That'd be multi-sensor ACC, basically. I think audi use something like "ACC plus".
2. This seems to discount what i just said, though, because GPS guided ACC should know better when it comes to exit lanes...
3. Imperfect system, I guess. It got spooked ;o)
4. Probably requires more time to confirm the target than the target is in front of you. It takes 1 second to cross your path, but perhaps would take more than 1 second to confirm that the object really is there.
5. It's absolutely meant to do this. It should be more cautious than you would be, so give it a go, I guess, and just be ready to slam the breaks on if it doesn't!

G

[Timothy Nathan]

I've got my car now, so my courage is diminished!

[BigAid]

Yeah can't say I'll be trying 4 either........


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[gbjk]

Meh - I'll give it a swing. I'm a bad enough driver normally that it wouldn't even constitute anything outside normal parameters.
That's the whole reason I checked all those options - It's far better than me being in control of the damn thing.

The only time I'm a good driver is when it's fast or complicated. Otherwise, it doesn't amuse me and I stop paying much attention.
If the damn thing would stop at red lights for me then that'd be one less serious hazard, too.

Don't worry, I'll tell you all my new numberplate so you can get the hell out of the way when you see it ;)

G

[Timothy Nathan]

Your red lights thing is a joke, but it would be nice if it recognised brake lights and anticipated....

[gbjk]

Probably not viable due to the inability to tell if it's a red light, or daylight lights on, or glare on the lights, or A US car indicating, etc.

[nealeb]

Was thinking about the oncoming car situation while driving earlier...

Easy enough - calculate closing speed from "radar" sensors and compare with road speed. If it's higher, then it's an oncoming car in the other lane and can be ignored - or someone turning across you... If it's slower, then it's a car ahead. Agree on the "won't overtake on the left" scenario. Haven't dared the "hammer up to stationary traffic" scenario either but it seemed happy with stop/start down from 70 to a crawl when I hit a bottleneck on a dual carriageway earlier. BTW, you have to watch it as you change lanes as it can "see" up the gap between vehicles ahead and starts accelerating and has to drop back again once it focuses on the car you're going behind.

I think that it might detect steering angle to know which direction to track on bends.

[BigAid]

Learnt something new - if in traffic - ACC stops, then ACC Go deactivates as been there 5seconds or so I've been restarting by using the Stalk - if you tap the accelerator it starts back into ACC too.....


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[Timothy Nathan]

Learnt something new - if in traffic - ACC stops, then ACC Go deactivates as been there 5seconds or so I've been restarting by using the Stalk - if you tap the accelerator it starts back into ACC too.....
I have just discovered a feature which is documented, but I had missed. We know that if you have been stationary for 3 secs, Automatic Go is deactivated, but if you pull the stalk at any time after that, including when the car in front remains stationary, Automatic Go is activated for the next 3 minutes. I haven't tried, but I assume, that if you pull the stalk as soon as you stop, you get the full three minutes.

[nealeb]

In the interests of economy, and the fact that I can look further ahead than the ACC "radar", I tend to brake before the ACC would do when approaching a queue at a red light, roundabout, or whatever. In fact, I often cancel the ACC in order to "lift off" on the approach. So I don't often find myself in the position of having ACC live when the last remaining car in front of me moves on to a roundabout. I had been warned by the salesman before a demo drive to watch out for this. Does anyone else find this a problem? I agree that trickling along slowly in traffic ACC works well, and for situations like a busy motorway, especially in a 50 limit roadworks section.

But this might be why ACC defaults to "3 sec stop and ACC self-cancels" - in case you at a traffic lights or about to pull on to a roundabout - but in a straightforward traffic queue, not at a junction, selecting the 3 min auto-go makes sense. So maybe there's a good reason why it works this way!

[Timothy Nathan]

I must say that I can't get it to wait three minutes. 15 secs is about the best I can get. I wonder if I have misread the manual.

It's quite difficult to test, of course, because you cannot when the car in front is going to move.