ACC failed.

[FelisBengalensis]

 .....and they’re easier to fix without a degree in computing required too. 

[Bud]

Having a degree in computing doesn't enable you to fix anything other than fries and a shake, or am I mixing that up with Business Studies?

[nicknorman]

I have found the ACC to be entirely reliable, with the design caveats I mentioned earlier (stationary traffic or coming up behind something with a large speed difference). One other time you have to watch it is at a give way point (junction, roundabout) since if the car in front moves off, the ACC will do the same regardless of whether there is a car coming that you need to give way to.

[rtj70]

I think people need to realise this is cruise control that can adapt to slowing cars in front. This is not a form of auto driving which is some way off and probably a long way off.

 

If the car in front drives through a junction your car will follow. If the car in front drives over the edge of a cliff - your car will follow. There is no intelligence behind how this works.

[IJWS15]

The ACC works fine if you are already following a car at similar speeds, I have concerns about it when you approach something travelling much slower or stopped especially at the lower interval.  By the time it starts braking you are very close.

 

Mine is manual so doesn't work at low speed.

[Howardv]

At higher speeds I always use a "longer distance" setting on the ACC, and find this to work well. On the closer setting the car starts breaking to late when closing up on slow traffic.

[aldouk]

The only downside for me on this is

• less economical
• If your stationary in traffic for a set period of time, it doesn’t start off on your own so cars behind me wondering what’s going on!

 

Otherwise it’s a good system but I do still hover over the brake pedal until I get to trust it more. 

[xman]

2 hours ago, aldouk said:

The only downside for me on this is

• less economical
• If your stationary in traffic for a set period of time, it doesn’t start off on your own so cars behind me wondering what’s going on!

 

Otherwise it’s a good system but I do still hover over the brake pedal until I get to trust it more. 

 

It is  cruise assist - nothing more. Just because it can do a passable party trick of poor mans traffic jam assist is not a good reason to "trust" it. It is not autonomous driving but crash avoidance in a moving traffic situation.

 

Don't "trust" it ever, otherwise you could end up smashing into a stationary or slow car.

[rtj70]

The reason why it cannot detect stationary vehicles in the distance (or just much slower cars) is because of the range of the RADAR used. It is short range and won't be that powerful. Which is why Tesla try to rely on cameras but they have their failings too - remember the car that went under the trailer in the US?

 

The same RADAR used for ACC is used to auto-brake at lower speeds but the key is lower speeds. LIDAR provides better scanning of surroundings, especially 16 channel LIDAR but (a) it's expensive and (b) not much use in the rain.

 

Which is why we won't have truly self driving cars for a long time.

[nicknorman]

46 minutes ago, rtj70 said:

The reason why it cannot detect stationary vehicles in the distance (or just much slower cars) is because of the range of the RADAR used. It is short range and won't be that powerful. Which is why Tesla try to rely on cameras but they have their failings too - remember the car that went under the trailer in the US?

 

The same RADAR used for ACC is used to auto-brake at lower speeds but the key is lower speeds. LIDAR provides better scanning of surroundings, especially 16 channel LIDAR but (a) it's expensive and (b) not much use in the rain.

 

Which is why we won't have truly self driving cars for a long time.

Not quite. It cannot detect slow moving cars ahead in time, due to the radar range as you say. But the reason it can’t detect stationary traffic is more fundamental - it relies on Doppler shift to differentiate between moving traffic, and other objects such as street furniture and barriers on sharp bends etc. Doppler shift and a knowledge of its own speed of course. Returns from static objects have a Doppler shift commensurate with its own speed. The Doppler shift from moving traffic will be different, and so this can be identified as vehicles. But the system can not differentiate between stationary vehicles and static objects as the Doppler shift will be the same.

[xman]

I think you'll find it doesn't react to stationary objects is for a fundamental design reason. The radar has a 12 degree angle and with that and when you go round bends etc, the radar receives bounces from roadside furniture either at the side or in the middle (keep left bollards etc). So it would constantly react to objects apparently drawing near. So the solution is to ignore objects not moving in the same direction and below a certain speed.

 

It does get caught out by cars turning off on front of you, a common observation.

 

Nick beat me to it by a second!

Edited 17 January, 2018 by xman

[rtj70]

So how does it detect stationary cars when using traffic assist?

[nicknorman]

9 hours ago, rtj70 said:

So how does it detect stationary cars when using traffic assist?

Because it’s tracking the car in front, it can observe a return whose Doppler shift equates to it slowing down and becoming stationary. Assuming the car hasn’t teleported away the only explanation is that it has stopped. In other words, if you are close behind a car that slows down and stops, that is fine. But if you are 100yds away round a corner and the same car ahead slows down and stops so that by the time it gets into range it is already stationary, it will not be detected. The radar needs to “see” the car whilst it’s still moving.

Edited 17 January, 2018 by nicknorman

[xman]

Traffic assist requires the front mounted camera.

[rtj70]

6 hours ago, nicknorman said:

Because it’s tracking the car in front

 

It's not only cars it will break to avoid a collision - try driving at a stationary object and the front assist will start warning you are near with parking sensors. But if you turn off front assist (or have an MQB based car that doesn't even have front assist like my previous car, an Audi A3) then the front sensors will not do anything when driving forwards and you get near something. 

[nicknorman]

24 minutes ago, rtj70 said:

 

It's not only cars it will break to avoid a collision - try driving at a stationary object and the front assist will start warning you are near with parking sensors.

But only if you are going pretty slowly in the first place. Try driving at a brick wall at 30mph. And before you do, make sure your insurance is valid!