Hi - dealer just disconnected my autonomous driving system that automatically adjusts speed to match changes in speed limits. In numerous circumstances, the system will "read" a speed limit on an adjacent road and unexpectedly accelerate/ decelerate. This is particularly unsafe when on the highway cruising at 70mph and the system reads an adjacent 40mph and basically slams on the brakes. Dealer said its a "known issue" and only fix right now is to disconnect system. Given how expensive this feature was and the fact that we specifically identified a vehicle with this safety system, we are frustrated by the lack of quality.

Anyone else have this issue?

 

You can turn it off in your driver assistance settings. This was the first thing that I turned off. The next is the lane keep assist (LKA). Useless nannies for me but may be helpful for others.

 

Given I live in rural area and can do long stretches of roads the technology to catch changes in speed limits is useful - but flawed so turned off.

 

That's right. You can turn this off. I had the awful experience when the car tried to go from 70 MPH to 25 MPH by reading a sign over the ramp. Such a half baked technology.

 

I does it to me on several sections of I69 where there are no exits and no signs. I don't know where its getting the bad data from but a simple check constraint would have prevented the problem. There are no interstate highways where the speed limit is 40 MPH.

Garbage In, Garbage Out (GIGO)

 

Here in PA it's not uncommon to see a 40 mph sign in a 55 mph and over stretch undergoing extensive repairs.

 

As mentioned above, the automatic speed limit adoption can be turned off in the settings. If it's turned off, you can manually adopt the current speed limit by pressing RESUME. This will set the current speed limit as the DISTRONIC set speed. This is how I use it. I set the initial speed to the speed limit and then increase it by the usual 10mph to 20mpg based on traffic flow. If the speed limit changes and I want to adopt it as the new set speed I press RESUME again.

There are checks in place to try to ensure it reads the correct speed limits. For example it factors in the GPS position and the road that puts you on based on the map data to try to resolve conflicting speed signs. For example frontage roads vs highway. However, while GPS accuracy can be as good as 10 to 16 ft, in real-world conditions when there are obstacles like buildings and trees the accuracy can decrease to 33 to 66 ft, that's 3 to 6 lanes off, so it could think you are driving on the frontage road when in fact you are driving on the adjacent highway. Also, if it doesn't see a speed limit sign for a while, it falls back to the map data, so if the map has incorrect speed limits for particular roads and there are no speed limit signs then it might adopt a lower speed limit, because it thinks that's the speed limit according to the map.