ACC on Smart Motorways

[fire_in_ldn]

Hi All,

Starting to make my first long journeys in the car. Noticed some worrying behaviour from the ACC yesterday. Have searched and can't find mention of this.

We were driving on the M4 which had 'Smart Motorway' signs turned off. When the car passed under some of these signs it would 'detect' a 50 mph zone and suddenly put the breaks on. I can't tell:

- if it happens on every sign
- if it's reading the blank sign as 50
- if it can't read the blank sign so defaults to 50
- if its getting some sort of message from the sign

Any ideas?

[Goaty]

Hi - yes, the auto speed detection in conjunction with ACC is often unreliable; I regularly travel up the A3 where it reads the 30mph signs on the residential roads running parallel with the 50mph part as you head into / out of South London and it assumes that’s the speed I should be going at, until it sees another 50mph sign.

I’ve completely disabled the auto-speed adjustment function and take control of what the max. speed is, myself (ACC still functions with automatic braking, acceleration and appropriate distance-keeping, up to the speed that I set, rather than what it’s read itself).

Elon, this country is a LONG way from the conditions you need for fully autonomous driving!

[RichR]

ACC uses a combination of the camera and the map data. Sometimes it gets it wrong - which is why it's only classed as a 'Level 2 driver aid' in the Enyaq and not self driving as such. Legally you're responsible for driving the car and correcting it when it gets it wrong. Quite often the map data is incorrect as the speed limit on a road isn't available on a national database, it relies on people updating the map data manually. I know of a few places near where I live where it's incorrect (though you can submit corrections via Here Maps).

I've had similar circumstances when it gets it wrong, especially on minor roads where the speed limit is less clear (eg entering a village that doesn't have 30mph signs, but does have lamposts close together indicating it probably is a 30mph zone). I suspect the map data indicates a 50mph in the absence of signs saying it's a national. So when you enter a new segment of road it's dropping to what it thinks is the correct limit.

When it happens, I just tap the cruise stalk up or down a couple of times to restore it to the correct speed. One tap = 5mph up or down.

[fire_in_ldn]

Hi - yes, the auto speed detection in conjunction with ACC is often unreliable; I regularly travel up the A3 where it reads the 30mph signs on the residential roads running parallel with the 50mph part as you head into / out of South London and it assumes that’s the speed I should be going at, until it sees another 50mph sign.

I’ve completely disabled the auto-speed adjustment function and take control of what the max. speed is, myself (ACC still functions with automatic braking, acceleration and appropriate distance-keeping, up to the speed that I set, rather than what it’s read itself).

Elon, this country is a LONG way from the conditions you need for fully autonomous driving!

Interesting thanks. Is that through one of the Database dongles or can you disable it in the car menu?

[fire_in_ldn]

ACC uses a combination of the camera and the map data. Sometimes it gets it wrong - which is why it's only classed as a 'Level 2 driver aid' in the Enyaq and not self driving as such. Legally you're responsible for driving the car and correcting it when it gets it wrong. Quite often the map data is incorrect as the speed limit on a road isn't available on a national database, it relies on people updating the map data manually. I know of a few places near where I live where it's incorrect (though you can submit corrections via Here Maps).

I've had similar circumstances when it gets it wrong, especially on minor roads where the speed limit is less clear (eg entering a village that doesn't have 30mph signs, but does have lamposts close together indicating it probably is a 30mph zone). I suspect the map data indicates a 50mph in the absence of signs saying it's a national. So when you enter a new segment of road it's dropping to what it thinks is the correct limit.

When it happens, I just tap the cruise stalk up or down a couple of times to restore it to the correct speed. One tap = 5mph up or down.

I'd be amazed if the map data had the motorway listed as 50mph in those sections though. It seems too much of a coincidence that it was happening after driving under the smart motorway signs. I think there must be some sort of incorrect read of the signs going on.

[Goaty]

Hi - it can be disabled in the car menu. I don’t remember exactly where but will check later unless someone else beats me to it.

[Pict]

viewtopic.php?t=1608&start=10#top

See my post about 1/2 way down in that thread

It is called speed preview

What speed was displayed in the driver screen at the times you were slowing down? I wonder if there were roadworks at on point and the speed limit has not yet been lifted when they were removed

I couldn't find a way to link to an individual post

[snalbansed]

This is particularly a problem in roadworks with an average speed check zone of 50, but a speed limit of 10 mph within the roadwork area just to my right!

However, contrary to some reports, I don't find it doing any sudden braking, and as long as I'm half concentrating I can quickly correct it using the stick to override without any major excitement.

So for me, I've found the ACC to be really nice to use, and the auto speed limit function to be fallible but still more useful than not.

Now what I would like it to do it to slow down a bit earlier (yes I know about the distance options, and I do make use of that) and to not accelerate towards stationary traffic only to suddenly slow down again

[RichR]

I know what you mean about accelerating toward stationary traffic - very disconcerting when you come off a slip road and meet the traffic queuing at the roundabout, but it's never actually crashed into anything (yet).

I too don't find it brakes excessively - if it starts to slow down or speed up where I don't think it should, just tapping the stalk a couple of times resolves it.

[fire_in_ldn]

I know what you mean about accelerating toward stationary traffic - very disconcerting when you come off a slip road and meet the traffic queuing at the roundabout, but it's never actually crashed into anything (yet).

I too don't find it brakes excessively - if it starts to slow down or speed up where I don't think it should, just tapping the stalk a couple of times resolves it.

Yep i've had the same acceleration issue!

Wouldn't say the break is excessive but still undesirable and not the safest when you're travelling at 70!