Another good example of how these systems can contribute to inattention on the driver's part figuring the car will take care of it. They're driving aids, not an excuse for not paying attention.

 

You don't get the point. Its not a matter of attention but of trusting the system.
One has to trust the system to use it at all. I'm not describing situations with lack of attention.
The issue is when to not trust the system. It turns out to be quite trustworthy in slow stop and go for example.
But in the example given one can't trust it to consistently perform well in my opinion.

 

A good motto is "Trust with skepticism and verify".

I have experienced the same scenario in the new gen2 Volt with ACC. I have some three years of driving experience with the 2013 Ford Fusion Energi with ACC. In the Fusion Energi with Eco-Cruise turned on its much slower (compared to the Volt with ACC) to accelerate when the gap becomes instantly large and its also slower to react when it becomes instantly small. Eco-Cruise essentially dampens the behavior of the acceleration so this scenario happened less often in the Fusion. Regardless, I keep my foot over the brake pedal ready to press during situations as you describe.

Another scenario I have experienced is rapid acceleration changes following a car in front through sharp curves at 25 mph. The car in front is going 15 mph to negotiate the curve and the Volt is too. Once it stops "seeing" the car ahead due to the curve the Volt starts to accelerate back up to 25 mph which is not appropriate for the curve. In that situation I cancel ACC. The manual clearly states this is a limitation of the current system.

From my private pilot days, I recall the mantra... "I am pilot in command" which means I am responsible for anything and everything that the airplane does regardless of autopilot settings, equipment failure, weather or ATC. For example, I would practice equipment failure scenarios with an instructor such as a run-away auto trim tabs failure. You had to be ready for anything.

I am still learning the nuances of the Volt ACC. So far I like the full stop and one button resume from a stop. I haven't heard the "go notifier" yet because so far I have been attentive and go. As I become familiar with the limitations of ACC in these vehicles, it makes me as alert as ever knowing there could be situations the system cannot handle. Hence, trust with skepticism and verify.

 

From my private pilot days, I recall the mantra... "I am pilot in command" which means I am responsible for anything and everything that the airplane does regardless of autopilot settings, equipment failure, weather or ATC. For example, I would practice equipment failure scenarios with an instructor such as a run-away auto trim tabs failure. You had to be ready for anything.

Despite all the requirements to check enroute and terminal weather forecasts for the primary and alternate destinations, I've always remembered my flight instructor's advice that "the weather is what you see out the windscreen". In other words, take all the written stuff with a grain of salt and make your decisions based on what's actually happening. This seems to me to apply to the safe operation of ACC.

As I said in another post, we're in for "interesting times" on the path to full automation as cars are equipped with more and more driving aids, each of which will have specific limitations that at least some drivers are bound to ignore. A driver is just as responsible for the safe operation of his vehicle as a Pilot In Command is his aircraft, but unfortunately few drivers seem to treat the responsibility with as much respect as most pilots do.

 

The idea that a "speed-up, slow-down, speed-up, slow-down" driver in front of me is effectively controlling my car speed does not get me excited about ACC. Perhaps I'm missing something having not experienced it's operation.

 

Understanding the limitations of any vehicle is the responsibility of the operator. ACC cannot handle panic stops or stopped cars. Deal with it.

 

I think it's more likely ACC will stop the car than you will. ACC samples at something like 5000 times per second, so it's not possible for the car ahead to slow down from 70 MPH to 10 MPH without the ACC system noticing. Maybe you need to adjust the following distance for your driving area?

One thing I have noticed is that my wife will get nervous and hit the brake which disengages the ACC before she gives ACC a chance. I trust the system and don't hit the brakes. We both stop but my stop is considerably smoother.

The only time ACC doesn't work is on twisty roads. Better to just leave it off under these conditions.

 

I think it's more likely ACC will stop the car than you will. ACC samples at something like 5000 times per second, so it's not possible for the car ahead to slow down from 70 MPH to 10 MPH without the ACC system noticing.

Yes, it is, if the cars moved far enough ahead to be out of the ACC's range, then stopped prior to coming back into range. That's the scenario being discussed here.

I love my ACC, but one place that I will manually override the braking is when I exit the freeway, and there is traffic waiting at a red light at the end of the off ramp. I find the ACC waits too long to brake, and then brakes way too hard for my liking.

The ACC (and frontal braking assist) is designed to ignore objects that are stopped, because the car can't tell if the road curves, or if there's a T-intersection, or whatever. It waits until it sees a real and immediate risk of collision and then gives warning. Otherwise, the building in front of you at the curve in the road would either cause the ACC to slow down and stop in the road, or cause the collision warning to scream at you all the time.
Same scenario for a car in the breakdown lane on a curving section of freeway. It will look like it's in front of your car for a while, then curve out of the way as you turn. If the ACC and braking assist weren't designed this way, they'd stop you in a traffic lane.

If the car ahead leaves the ACC sensor's range and then stops before coming back into range, the ACC will ignore it until an impending collision, then scream at you at the last minute. That's how it has to be designed.

 

DonC,

I'm talking about situations where the FAB activates and the 5 red LEDS light up on the windshield.
Since the manual says that FAB is designed to reduce the severity of crashes, not prevent them, I've thought it was prudent to brake as quickly as possible at that point. Do you have a different perspective?

The issue is what happens when the following distance gets much longer than the programmed distance and then the car ahead jams on its brakes. As Alan suggested, I think the Volt has lost tracking on the car ahead at that point so its not a matter of programmed following distance. It may well be, however that if the ACC were set at or above the speed that the car ahead reached there would be no problem if it suddenly slowed. I'm just reluctant to set the ACC for 75 or so when I'm in slow stop and go traffic.

Using your method do you see the FAB activate?

 

The issue is what happens when the following distance gets much longer than the programmed distance and then the car ahead jams on its brakes. As Alan suggested, I think the Volt has lost tracking on the car ahead at that point so its not a matter of programmed following distance. It may well be, however that if the ACC were set at or above the speed that the car ahead reached there would be no problem if it suddenly slowed. I'm just reluctant to set the ACC for 75 or so when I'm in slow stop and go traffic.

Using your method do you see the FAB activate?

The most common situation when I see the FAB activate is when someone cuts right in front of me and the following distance goes from safe to very unsafe. But the car always stops itself. And it sees things before I do. My comment was based on the fact that initially my wife would hit the brake and disengage ACC when the ACC had everything perfectly under control. I kept telling her to let the car stop and she kept telling me that it wouldn't stop in time. As with blind spot warning, she had to learn to trust the technology.

In any event, I've never needed to brake even when traffic has come to a sudden complete stop. You may want to take the car in and have its ACC system checked out. Without being in the car it's impossible for me to say if your system acts like mine.

 

DonC,

Thanks for the info.

I'm wondering what following distance setting you use.
We are using the medium distance setting but as you suggested earlier maybe a longer distance would help.

 

I love my ACC, but one place that I will manually override the braking is when I exit the freeway, and there is traffic waiting at a red light at the end of the off ramp. I find the ACC waits too long to brake, and then brakes way too hard for my liking.

 

Alan,

I don't think the car ahead has to be completely stopped in this scenario. Just out of range and then quickly brake to a low speed so its a very large speed differential.
Anyway, thanks to you and DonC I think I see how to even better adjust our driving to accommodate the benefits and new hazards of assisted driving with the Volt.

 

I noticed that hills also throw it off. I made it to the top of a hill, and while I could see right away that I needed to stop, the Volt began accelerating down the hill until I quickly hit the brakes. I think it sees clear space in front of it, the radar is tunnel-visioned straight ahead (even if straight ahead is the sky).

 

Hey here's an idea...how about you DRIVE your CAR and be in CONTROL.

I rarely use the lane keep assist, and even then I only use it while on long highway drives.

Why would you "trust" the ACC system in the example OP gave on the first post? Sounds ridiculous to me. Drive your car and don't be a hazard to others because you are randomly "trusting" the ACC.

 

Let the record show that the OP, me, never mentioned LKA, which I consider almost useless.
Let the record show that I have not been shouting.
Let the record show that in exploring the functional parameters of my new volt I have not crashed it or come close to crashing it and posted here to get other's experiences.
Let the record show that I have never implied that, and have not, in the driving described in the OP been less than fully attentive to driving.
Let the record show that, as I said earlier in a different manner, there is no absolute trust being considered. Trust is conditional on one's evaluation of the total situation. One cannot live without trust. One cannot drive without trust. Without a degree of trust the ACC is useless.

Are you guys are conflating my questions and concerns with some of the ridiculous accidents reported with the Tesla autopilot?
Well, its not appropriate. Just cool your jets and be civil.

 

I got it!
One big motivator for keeping this thread going was to get to 100 posts for senior member status.

 

I got it!
One big motivator for keeping this thread going was to get to 100 posts for senior member status.

Congrats! Steverino will be sending out your t-shirt soon. Welcome to this exclusive club.

 

Let the record show that as an owner of the wonderful 2017 Volt with ACC, I categorically agree with everything the OP has said. GM *must* adopt Tesla's practice of judicious over the air updates to iteratively improve the quality and safety of this wonderful but IMO dangerously limited system.

 

What is confusing to me is that GM has had ACC on a variety of vehicles for years so there must be a lot of hardware and software "customization" (for the lack of better word) otherwise it would have been on the first GenII's like my wife's Volt or the first GenI of the Bolt. I would have liked to have the Volt's ACC when she first got it and I was roadtripping it. ACC (aka TWCC) on my other car has added a much more relaxing drive to several roadtrips and the rare stop-n-go that I am in.

 

Just to clarify, this issue just crops up for us in a very particular situation.
Slow stop and go punctuated with brief bursts of "normal" high speed.
It works great for normal slow stop and go and for normal freeway driving at speed.

But in this one situation it will sometimes wait till quite late to activate FAB, etc.
It seems as though what is happening is that the Volt is losing contact with the leading vehicle which one should be able to monitor if one watches the dash instead of the road (There is a lot of information about what is happening presented on the display but to see it one has to look away from the road to see the small symbols). (The manual says that the FCA only goes out to 197 feet and I assume that applies to ACC, etc. as well.) Then it fails to detect the slow moving vehicle ahead once it quickly slows. (the manual says it may not detect stopped or slow moving vehicles.) And since the speed of the Volt is fast at this point it comes uncomfortably close to the leading car before activating FAB and FCA. Then when one jumps and slams on the brakes the first thing that happens is that the vehicle jumps ahead in the transition before manual braking takes over. Doubly scary.

I think that a longer detection distance might help.

For us the solution at the moment is to take over manually after such high speed bursts in stop and go traffic.

I too find it puzzling that there is this issue in what is not cutting edge technology in the auto world or for a manufacturer that is testing self-driving cars.

 

But in this one situation it will sometimes wait till quite late to activate FAB, etc.

That's because FAB is not a normal driving aid - it's an emergency avoidance feature. If FAB activates then it probably means that you should have already been pressing the brake pedal.

 

Ideally, there will be communication between vehicles.

The vehicle ahead could share information with the vehicle behind. I suppose that's what brake lights do, but it could be much more sophisticated than that. Especially if all the vehicle were autonomous and shared there near term plans with the vehicles around them.

 

There's been a lot of discussion about this. I suspect future autonomous cars will use some sort of swarm logic and pass data to one another about both what they can see and what they are doing. I'm not sure it's practical or helpful for a car with adaptive cruise and lane keeping at the Volt's level, though.