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View Full Version : Active Cruise Control....will it prevent you from an accident?


CarBrain
10-05-2010, 08:52 PM
From reading the function of this option, it seems that a car with Active Cruise Control will stop or slow down and put a space from your car to the car in front of you.

So for instance, if the car in front of you make a sudden stop, would the car quickly and automatically slow down and even "break on a dime" to prevent you from rear ending the car in the front? Would it be faster than a human reaction ?

tunafish
10-05-2010, 09:43 PM
From reading the function of this option, it seems that a car with Active Cruise Control will stop or slow down and put a space from your car to the car in front of you.

So for instance, if the car in front of you make a sudden stop, would the car quickly and automatically slow down and even "break on a dime" to prevent you from rear ending the car in the front? Would it be faster than a human reaction ?

While driving (fast) in the left lane of the autobahn, a slower car suddenly pulled into my lane. My car braked hard, the red "car" symbol appeared, and an audible warning sounded. It was faster than my reaction, but probably because ACC tries to maintain a somewhat greater spacing between cars than I am used to. There are likely a lot of factors involved, such as the time it takes to recognize that a car is in your lane. I also suspect that the ACC never brakes as hard as driver in a panic stop.

CarBrain
10-05-2010, 09:55 PM
While driving (fast) in the left lane of the autobahn, a slower car suddenly pulled into my lane. My car braked hard, the red "car" symbol appeared, and an audible warning sounded. It was faster than my reaction, but probably because ACC tries to maintain a somewhat greater spacing between cars than I am used to. There are likely a lot of factors involved, such as the time it takes to recognize that a car is in your lane. I also suspect that the ACC never brakes as hard as driver in a panic stop.

But do you think the car will break or slow down to the point where it would not touch the car in front of you.

If the ACC is smart enough, would it be able to calculate the car in front as being in a dead stop or just slowing down and make the appropriate adjustment in breaking the car accordingly.

eaglesrest
10-06-2010, 02:25 AM
If you approach an untracked car at a dead stop ACC will not stop you. You have to break manually. If you are tracking a car that slams on to a dead stop the car will stop as efficiently as it can while maintaining a safe distance. There are limits but I expect you'd need some nerve to try and find them ;)

pharding
10-06-2010, 04:20 AM
The ACC equipped F10 is quite remarkable in its ability to stop. I have used it extensively in a variety of situations for 2000 miles with many miles in stop and go heavy expressway traffic. It works amazingly well in picking up any vehicle including motorcycles and cars that jump in your lane. It is quicker than a human driver. The biggest danger of a crash with it occurs when you accidentally touch the brake or pedal while it is on, turning it off unnoticed by you. You assume that it is on. When a braking situation arises, you assume that it is on. You are then slow to realize the problem and initiate braking. Stop and Go ACC works much better with HUD because the critical information is right on your windshield. It is a "must have" option, however I would definitely get HUD with it if you intend to use it a lot in urban expressway traffic.

listerone
10-06-2010, 07:09 AM
But do you think the car will break or slow down to the point where it would not touch the car in front of you.
In spite of all the ooohs and aaahs I've read about ACC (including in this thread) I think it's unwise to depend on it to stop you safely and effectively *every* time and in *all* situations.When I order my F10 (hopefully next summer when the diesel is supposed to arrive) I'll be getting ACC but I'll think of it as an extra level of safety rather than something I can set and then forget about watching the road or thinking about the brakes.

quackbury
10-06-2010, 07:40 AM
From what I have read on this thread and elsewhere, ACC "tracks" the car ahead of you. OTOH I am usually "monitoring" brake lights farther down the road.

If the driver ahead of you is attentive, I would imagine that ACC is more than adequate to bring you to a safe stop before you hit him. But if the driver ahead of you is texting / eating breakfast / reading the paper / putting on makeup (all of which I see on my morning commute) and rears ends a stopped semi, I doubt ACC will save your azz. (And even if the car does manage to stop in time, there's a good chance the guy behind you won't).

While I think the concept of ACC is neat, over time I worry it could lull you into a false sense of complacency. (I hadn't even thought about it being inadvertently de-activated, as pharding noted).

schlagle
10-06-2010, 08:50 AM
Nobody seems to be worried about the car behind them. If ACC acts faster than a human doesn't it run the risk of increasing your likelihood of getting rear ended in tight traffic? Rear end collisions account for 75% of highway accidents.

In tight traffic I may want to stop or slow closer to the vehicle ahead of me if I'm worried about the yahoo behind me. This saved my rear just yesterday actually. Well, that and a quick tug to the right to give the inattentive mom in the minivan behind me time to change lanes.

quackbury
10-06-2010, 09:00 AM
Nobody seems to be worried about the car behind them. If ACC acts faster than a human doesn't it run the risk of increasing your likelihood of getting rear ended in tight traffic? Rear end collisions account for 75% of highway accidents.

In tight traffic I may want to stop or slow closer to the vehicle ahead of me if I'm worried about the yahoo behind me. This saved my rear just yesterday actually. Well, that and a quick tug to the right to give the inattentive mom in the minivan behind me time to change lanes.

+ 100. I have been rear-ended HARD 4 times. 1 of those times my car was totalled (Audi Coupe), 2 other times, my cars should have been totalled (Mercedes C280 and C43 AMG) as they were never "right" again.

3 out of the 4 situations were because my car stopped better / faster / shorter than the jalopy behind me. (The 4th time the other driver had a blood alcohol level of 0.2, so the quality of the braking system wasn't an issue). That's why I try to look FAR down the highway and plan accordingly, while monitoring the rearview. As good as ACC may be, I imagine there are technical limits on both those fronts.

richschneid
10-06-2010, 11:41 AM
When I picked up my car on Monday the person teaching me about the car went into the iDrive and set the "frontal collision" avoidance setting. It has two settings. It will slam on the brakes to a full stop to prevent a frontal collision even with the ACC turned off. I will have to check the owners manual to be sure about this. I set it to the more sensitive setting.

richschneid
10-06-2010, 12:27 PM
Checked the owner's manual page 107. Collision warning is effective if the button on the left side of the dash is pushed and lit. It works even when the ACC is off. It brakes but DOES NOT BRING THE CAR TO A FULL STOP. But it will sound and alarm and flash red so you can hit the brakes. The time of prewarning can be set with the iDrive.

Ry"c
01-01-2011, 09:04 PM
The Collisinon Avoidance system is remarkable life- and property damage-saving feature that is new for 2011 and only available on the 5-Series with Active Cruise and some other carmakers' autos. Why is it not touted more...should be a big selling point for deciding to purchase or lease a 5-er over a 7 or 3. A huge reason for adding active cruise to a purchaser's choice of options in an F10 would be to get this safety feature. Not sure why it is not advertised and promoted more. Has anyone made a comprehensive list of other automakers that have this...I note some 2011 Infinitis and Ford Taurus have it. Any other manufacturers?

AzNMpower32
01-01-2011, 09:46 PM
Checked the owner's manual page 107. Collision warning is effective if the button on the left side of the dash is pushed and lit. It works even when the ACC is off. It brakes but DOES NOT BRING THE CAR TO A FULL STOP. But it will sound and alarm and flash red so you can hit the brakes. The time of prewarning can be set with the iDrive.
Correct. The Collision Warning is included with ACC but must the switched on via the dash switch on the left side. Adjustments can be made in iDrive as to the pre-warning distance without influencing the ACC pre-warning.

pharding
01-01-2011, 10:06 PM
Active Cruise Control and Collision Warning....will it prevent you from an accident?.
No it will not. It is a great option "when" it picks up the car in front of you. Unfortunately it does not always do so. It is a tool, but it is not a substitute for fine driving skills. My wife and grown kids hated it when we drove 200 miles and back to see our families at Christmas. When approaching stopped cars at 65 mph it does not always see the stopped cars in order to apply the brakes. I like the option and the warning system a lot, but it is not a substitute for being alert. Actually it can give you a false sense of security which will be dangerous for some drivers.

tunafish
01-01-2011, 10:21 PM
No it will not. It is a great option "when" it picks up the car in front of you. Unfortunately it does not always do so. It is a tool, but it is not a substitute for fine driving skills. My wife and grown kids hated it when we drove 200 miles and back to see our families at Christmas. When approaching stopped cars at 65 mph it does not always see the stopped cars in order to apply the brakes. I like the option and the warning system a lot, but it is not a substitute for being alert. Actually it can give you a false sense of security which will be dangerous for some drivers.

It has pluses and minuses. For most highway cruising situations, it is great. I have also experienced the situation that pharding mentioned. When approaching a stopped car, my car continued at a high rate of speed until it was almost too late (well, I thought it was almost too late). I couldn't tell for sure since I chickened out and applied the brakes. It may well have stopped itself in time, but who wants to take the chance. Perhaps some more software tweeks are needed. The other problem arises when you actually do want to overtake someone. You have to remember to give it gas, otherwise you slow down gradually. With practice, you learn its good and bad points. Overall, I like it.

Rafa
01-01-2011, 10:32 PM
As I would expect, just about every person in this forum is an attentive driver, cognizant of the traffic around and not prone to let the safety systems completely take over in an emergency situation. That is a very good thing, needless to say. BMW's collision avoidance system will warn you and even apply the brakes, but like any other such system it has limitations and is far from perfect as the state of the art in collision avoidance systems is far from perfect. Furthermore, BMW's system does not detect pedestrians that might cross your way (Volvo does, but again, their system has limitations as well). Also, I believe that BMW's system does not even apply 100% of the braking force, just 80%. Clearly, BMW's system is intended to assist the driver and react earlier than the driver might, but it is not intended to avoid a collision altogether, although it conceivably could under some circumstances. The driver is supposed to take over and regain manual control of the car as soon as possible.

Rafa
01-01-2011, 10:46 PM
When approaching a stopped car, my car continued at a high rate of speed until it was almost too late (well, I thought it was almost too late). I couldn't tell for sure since I chickened out and applied the brakes.

It is a good thing you chickened out and applied the brakes in time. The manual states that the system will not detect stopped cars or other stationary objects.

I have approached moving cars and waited for the system to react. The warning comes on, but I also chicken out and apply the brakes before the system does. I wish I would go to the Performance Center in SC to test the system under controlled conditions in order to learn the limits and limitations of the system from a BMW driving instructor.

AzNMpower32
01-02-2011, 08:42 AM
I have approached moving cars and waited for the system to react. The warning comes on, but I also chicken out and apply the brakes before the system does. I wish I would go to the Performance Center in SC to test the system under controlled conditions in order to learn the limits and limitations of the system from a BMW driving instructor.
You could try with a traffic cone :p

Needsdecaf
01-02-2011, 08:55 AM
But do you think the car will break or slow down to the point where it would not touch the car in front of you.

If the ACC is smart enough, would it be able to calculate the car in front as being in a dead stop or just slowing down and make the appropriate adjustment in breaking the car accordingly.

Without a doubt absolutely not.

Ry"c
01-02-2011, 09:13 AM
The "Active Cruise with Auto Stop" was available beginning in the the 2007 model year. This slowed and then stopped the auto when the active cruise control was engaged and an obstruction moved into the path of the vehicle. The new feature for 2011 is the "Collision Avoidance" which was not previously available. This feature stops the car at any time, even if the cruise control is not engaged. This is a constantly-active life- and property-damage safety feature that determines if the auto is about to be in a collision and will warn the driver, pre-load the brakes and if needed stop the vehicle. For whatever reason, BMW has only made this an option available for the 5-Series and not for the 7-, 3- or 1-series.

BimmerUKF10
01-02-2011, 09:36 AM
ACC is great, but as other have said you cannot rely on it. When approaching a roundabout at speed when the vehicle in front is approaching a stop, it sometimes breaks too late and you have to intervene. The collision warning thing works! I've had it warn me on one occasion and it did break. Whether is would have brought the car to a stop I'm not sure. I breaked regardless - just not worth the risk to find out! Why the collision avoidance is switchable is beyond me. Can't see any reason for turning it off unless you purposely want to crash your car :-)

Overall though I find ACC very useful on the motorway - especially on long drives as it gives your right foot a rest. Would be better if BMW actually gave you somewhere to the right of the throttle to rest your foot though!

tunafish
01-02-2011, 09:48 AM
Somewhere on internet (maybe Bimmerfest?) I saw an official BMW test of an offset collision with and without the collision system activated (the ACC was NOT on either case). With the collision system inactivated, a 5-series car hit the barrier at about 40 mph. With the system activated, an identical car automatically braked at the last moment, reducing the impact speed to about 25 mph. I hope someone can find the link (I can't seem to) and re-post.

The take home message is that the collision avoidance system (which comes with ACC) doesn't prevent a crash, it just reduces the damage. The ACC, when on, can bring the car to a complete stop when approaching a stopped car ahead, most of the time, but I have had to intervene when things got too dicey.

tunafish
01-02-2011, 10:12 AM
Still can't find the video, but the description below comes from BMW Press Munich:


Every motorist is familiar with the situation: The end of a tailback suddenly appears behind a motorway bend. If a motorist is inattentive or visibility is impaired, a rear-end collision is imminent. after all, this is the cause of around 40 percent of all motorway accidents involving injured persons.

In order to defuse this kind of hazardous situation, some premium segment vehicles such as the BMW 5 Series are already equipped with anticipatory assistance systems that help reduce the risk of such accidents. BMW’s successful upper mid-range model, which was just recently brought to market, features – combined with Active Cruise Control – an optional rear-end collision warning system incorporating a braking function that activates an alarm scenario in two stages.

In the event of a potential collision with the vehicle in front, the driver is first given a preliminary warning by means of an illuminated red vehicle symbol on the instrument panel and on the Head-up Display. At the same time, the braking system is prefilled and the minimum triggering level of the hydraulic brake assistant lowered. This ensures that in an emergency brake pressure is built up faster when the driver applies the brakes, therefore significantly reducing the stopping distance.

If the danger of collision is acutely imminent, the second stage of the collision warning commences. In situations demanding particularly rapid intervention by the driver, the system activates an acoustic signal in addition to the visual warning. Should the driver still not react to the request to apply the brakes, a time-limited delay procedure is activated: The car brakes for 1.2 seconds with reduced deceleration, whereby speed is already reduced before the driver can apply the pre-tensioned brakes.

Based on the information supplied by the radar sensor of the Active Cruise Control system (ACC Stop &Go) featured in the new BMW 5 Series, the system detects when a collision can no longer be avoided by the driver’s reaction. In this case, an automatically activated emergency brake application function ensures that collision speed is, nevertheless, significantly reduced.

Based on a conventional EuroNCAP test with the car
approaching an offset obstacle at 64 km/h, a so-called offset crash, the vehicle used in the DEKRA test incorporating advanced brake intervention likewise initially accelerated to 64 km/h. However, immediately before impact the BMW 530d braked hard – as stipulated by the system – and collided with the offset block at a reduced speed of just 40 km/h.

Due to full brake application immediately prior to impact and the car’s pitching movement resulting from this, the vehicle changes its position, particularly when the front bumper hits the block. The vehicle collides with the obstacle in a slightly “lower” position than in the case of a crash occurring without prior application of the brakes.

Concerning the deceleration, occupants also assume a position further forward. More important, however: In the event of a crash incorporating prior brake application, the severity of impact is reduced considerably, thereby significantly lessening the strain on all occupants.

Needsdecaf
01-02-2011, 10:16 AM
The "Active Cruise with Auto Stop" was available beginning in the the 2007 model year. This slowed and then stopped the auto when the active cruise control was engaged and an obstruction moved into the path of the vehicle. The new feature for 2011 is the "Collision Avoidance" which was not previously available. This feature stops the car at any time, even if the cruise control is not engaged. This is a constantly-active life- and property-damage safety feature that determines if the auto is about to be in a collision and will warn the driver, pre-load the brakes and if needed stop the vehicle. For whatever reason, BMW has only made this an option available for the 5-Series and not for the 7-, 3- or 1-series.

As was said by tunafish, this will NOT completely stop the vehicle over a certain speed. It will only mitigate the crash by reducing the collision speed.

Bottom line, once you are over 25 MPH, none of the systems will brake you an emergency with enough force to completely avoid it.

quackbury
01-02-2011, 01:36 PM
As was said by tunafish, this will NOT completely stop the vehicle over a certain speed. It will only mitigate the crash by reducing the collision speed.



I don't know whether ACC will brake you to a complete stop or not, but I assume it "might" depending on the distance to the vehicle it is tracking. However I can think of several situations where I doubt it would do much / any good:


The vehicle ACC is tracking comes to a sudden stop - runs into a bridge abutment, rear-ends a stopped semi, etc.
You are approaching an intersection and a car on the perpendicular street runs a red light.

The biggest concern I have is ACC lulling you into a false sense of security. IMHO there is no substitute for looking down the road and having good situational awareness. (But I realize that there are many drivers who don't practice those skills - I see them every day on their way to work - and for them I guess this system is better than nothing).

As they say, build an idiot proof car, and they'll respond by building a better idiot.

h3m8n
01-03-2011, 02:44 AM
Active cruise is great. I have recently used it during a long road trip. It does stop the car if the vehicle in front is stopped. However, I dont know how fast it is able to react as I've only tested it in slow crawling traffic and not sudden stops. I have also used it and "somewhat" relied on it during the recent down pours here in Northern California. I use Active Cruise with the Night Vision cam during a downpour and a bit of Fog and I felt much safer knowing that I was at a certain distance away from the vehicle in front giving me some room to brake just in time. However, just like anything else, one shouldn't rely on tech alone, you need to be fully aware that systems malfunction so you always have to be on your toes. I have heard that it's not a good idea to use cruise control when it's raining. Is this true?

CC Brown
01-03-2011, 04:30 AM
I have used the Start-Stop ACC now for 4 months on road trips and heavy freeway traffic. It is a wonderful safety tool. A car must be moving for the unit to detect it and react. Otherwise it could see a stopped truck on the side of the road and slam on the brakes. I have had drivers in front slam on brakes and the ACC stops my car. I am not as worried about being rear ended because I use the 3 or 4 second setting on the interval distances. Most people follow too close and some don't like that the shortest interval is 1 second but driving courses like AAA recommend at least 3 sec. Because of this distance it gives the person behind you time to react also.

I have been given a warning 3 times. Each time was when a car turned from the lane to my left to cut across to make a freeway exit. When the radar is following the car in front and another car cuts in it takes a segment of time for it to recognize that. You need to be alert when this happens. When you are approaching a stop light with cars stopped it odes not see those stopped cars-know that! All of this is carefully explained in the manual!

Like the post that says the car will not stop on it's on when approaching a stopped object is correct. It will at the very last apply the brakes enough to make a less sever crash- like 60mph to 40mph. That could be enough to safe your life!

On road trips I feel much more secure and safe with it.

raleedy
01-03-2011, 12:49 PM
Will it brake or will it break? That's the question. ACC will avoid an accident, but not the accident you're going to have.

07X3platinum
01-04-2011, 08:21 AM
I plan on ordering ACC on my next BMW, but I only plan to use it during stop and go traffic. From a video I saw on YouTube, when the car comes to a stop (during highway traffic) you just have to push a button on the steering wheel to get the car going again. I love that! It makes traffic a lot less frustrating.

tunafish
01-04-2011, 08:28 AM
I plan on ordering ACC on my next BMW, but I only plan to use it during stop and go traffic. From a video I saw on YouTube, when the car comes to a stop (during highway traffic) you just have to push a button on the steering wheel to get the car going again. I love that! It makes traffic a lot less frustrating.

Note exactly. If the car stops for less than a few seconds, it will start moving again without doing anything once the car in front moves. If more than a few seconds, the display will show some moving bars, and you can re-start by just tapping the gas pedal. I don't think pushing the resume or set button will do it.

BimmerUKF10
01-04-2011, 12:28 PM
Note exactly. If the car stops for less than a few seconds, it will start moving again without doing anything once the car in front moves. If more than a few seconds, the display will show some moving bars, and you can re-start by just tapping the gas pedal. I don't think pushing the resume or set button will do it.

You have to apply gas and then press resume.

tunafish
01-04-2011, 12:38 PM
You have to apply gas and then press resume.

I have not found it necessary to press resume. I just touch the accelerator.

tunafish
01-04-2011, 12:39 PM
I have not found it necessary to press resume. I just touch the accelerator.

But maybe this is a US/UK difference.

BimmerUKF10
01-04-2011, 12:40 PM
I have not found it necessary to press resume. I just touch the accelerator.

I'll check that out tomorrow!

Rafa
01-04-2011, 04:42 PM
You have to apply gas and then press resume.

I just press the resume button and the car goes. I have not tried pressing the accelerator instead of the resume; I'll try that soon to see whether it works for me.