[MotoWPK]

Took delivery of our '19 x40i two days ago and had the opportunity for a couple of hours of highway time yesterday. This is my first experience with active cruise control and, of course, the lane assist, both of which I found worked very well. As anticipated, one must become familiar with their characteristics, one of which is that they do not act with the forecasting ability of a human driver. This arises from sensing limitations, e.g. the vehicle is not looking ahead as far as the driver does, and the vehicle also does not know the driver's future intentions. To this latter point I experienced a characteristic of ACC that is notable and wanted to see how others manage ACC in this regard.

Specifically, the first example is where a vehicle passes you and pulls into your lane at a close enough difference that ACC deacclerates but, due to the speed differential, it isn't necessary to slow down. Recognizing the speed differential I realize that the passing vehicle that has pulled into my lane will create an adequate separation gap quickly enough that slowing down isn't necessary.

The next example was proceeding along a four lane, but not limited access highway. In the left lane, there was a vehicle ahead in this lane, slowing to turn left. As I approached, on ACC, I initiated a lane change to the right. Mid-way through this maneuver the vehicle quickly deaccelerated, and I realized it was because of the proximity and speed differential to the vehicle ahead. Here again, I know there is no need to slow because I am in the midst of changing lanes and the reduced separation distance is very momentary.

This last scenario would also be encountered when, say, traveling in the right lane and approaching a slower moving vehicle in this lane. You see a vehicle approaching behind you in the left lane but correctly judge there is sufficient distance to pull into the left lane to pass the slower vehicle ahead. It's not unusual in such a situation that you may momentarily come closer to the slower vehicle ahead than normal, but again, it is not an issue because it is momentary. What could be an issue is if, unexpectedly, ACC decides, in the middle of this maneuver, to deacclerate now putting you at an unsafe speed to pull in front of the approaching vehicle behind in the left lane.

With conventional cruise control this isn't an issue, but with ACC one needs to learn and apply a different philosophy. At this point, with all of one day of ACC experience, it appears on must learn to, in these situations, deactivate ACC prior to initiating the maneuver, then resume once it's completed.

Anyone develop an alternate way to handle these situations?

[ggalanis]

Originally Posted by MotoWPK

Took delivery of our '19 x40i two days ago and had the opportunity for a couple of hours of highway time yesterday. This is my first experience with active cruise control and, of course, the lane assist, both of which I found worked very well. As anticipated, one must become familiar with their characteristics, one of which is that they do not act with the forecasting ability of a human driver. This arises from sensing limitations, e.g. the vehicle is not looking ahead as far as the driver does, and the vehicle also does not know the driver's future intentions. To this latter point I experienced a characteristic of ACC that is notable and wanted to see how others manage ACC in this regard.

Specifically, the first example is where a vehicle passes you and pulls into your lane at a close enough difference that ACC deacclerates but, due to the speed differential, it isn't necessary to slow down. Recognizing the speed differential I realize that the passing vehicle that has pulled into my lane will create an adequate separation gap quickly enough that slowing down isn't necessary.

The next example was proceeding along a four lane, but not limited access highway. In the left lane, there was a vehicle ahead in this lane, slowing to turn left. As I approached, on ACC, I initiated a lane change to the right. Mid-way through this maneuver the vehicle quickly deaccelerated, and I realized it was because of the proximity and speed differential to the vehicle ahead. Here again, I know there is no need to slow because I am in the midst of changing lanes and the reduced separation distance is very momentary.

This last scenario would also be encountered when, say, traveling in the right lane and approaching a slower moving vehicle in this lane. You see a vehicle approaching behind you in the left lane but correctly judge there is sufficient distance to pull into the left lane to pass the slower vehicle ahead. It's not unusual in such a situation that you may momentarily come closer to the slower vehicle ahead than normal, but again, it is not an issue because it is momentary. What could be an issue is if, unexpectedly, ACC decides, in the middle of this maneuver, to deacclerate now putting you at an unsafe speed to pull in front of the approaching vehicle behind in the left lane.

With conventional cruise control this isn't an issue, but with ACC one needs to learn and apply a different philosophy. At this point, with all of one day of ACC experience, it appears on must learn to, in these situations, deactivate ACC prior to initiating the maneuver, then resume once it's completed.

Anyone develop an alternate way to handle these situations?

You can use the throttle to get closer to the cars in front of you.
I do this when I want to pressure slow traffic in the left lane to get out of the way since the minimum distance the ACC allows is not close enough to pressure the car in front. Adding throttle input temporarily deactivates the radar part of the ACC. Although i don't distinctly remember using it in the scenarios you described above, I do think it would work just fine.

GG

[TurtleBoy]

As GG said, you can use the throttle. In the situation of the car slowing due to a vehicle turning, if there is no one behind me I sometimes just let it slow down but if there is someone I just hit a gas a bit. The same can be done in the passing situation, if you feel any slowing just hit the throttle a bit.

[gpitts]

You are experiencing the two halves of ACC in the distance scenario you describe. One part of ACC ensures a "safe" following distance is maintained, the other keeps your vehicle at the speed setpoint. The following distance portion of the algorithm has priority and is ensuring that distance is met. This is no doubt driven by liability concerns on the part of BMW.

[MotoWPK]

Applying accelerator to temporarily override the distance control - great tip! Thanks.