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Discussion Starter · #1 · (Edited)
Adaptive cruise control with Porsche Active Safe (PAS)

Available as an option, this cruise control function regulates your speed according to the distance between your vehicle and the vehicle in front. A radar sensor monitors the road ahead up to a distance of 200 m. If you have set a cruising speed but have begun to gain on the vehicle in front because it is driving more slowly, this is detected by the radar sensor.

The system now reduces the speed of your vehicle at a maximum rate of 3.5 m/sec2 by restricting the throttle or by applying the brakes appropriate to the prevailing situation until the distance that you have preset is maintained. Your vehicle will now continue at a reduced speed. If the other vehicle decelerates further, adaptive cruise control will continue to reduce your cruising speed – even down to a halt.

For additional safety, if the system detects that the distance from the vehicle in front is decreasing, it will also prepare your vehicle for braking by precharging the braking system so that the brake pads are already in light contact with the brake discs. However, drivers still have to perform heavier braking themselves. As soon as the road ahead clears again, your vehicle will accelerate back up to the cruising speed originally set.

If your vehicle approaches the vehicle in front too quickly, Porsche Active Safe (PAS) will issue audible and visual warnings. In addition, the system briefly jerks the brakes and if necessary initiates target braking, with any braking pressure applied by the driver being increased within certain system limits.
I purchased the PAS option on the Boxster under the justification that one careless bumper scape might cost me the $2k that the system did, assuming a high insurance deductible. What actually happened surprised me. You can read my original review of the system here at the bottom of the OP.

A few months ago I was in stop and go traffic in California. In particular, this was a whipsaw kind of stop and go where it's 0-50 and 50-0 repeatedly within the same highway mile, 12+ lanes wide with long term construction projects in the area taking up the breakdown lanes. A benefit of PAS seemed to be that it handled crawling traffic well, taking some of the agony out of driving. You steer and it does the gas and brakes, like a partially autonomous vehicle. If the road is straight you're just along for the ride. Over time you begin to trust the system more and correct/override it less and less.

Current generation vehicle sensor and sonar systems can only detect objects directly in the path of the vehicle (front, front-left, front-right, and on some cars side lanes). They can't, for instance, anticipate a traffic pattern that a human easily can. For instance if the car in front of you is going 50 MPH but you see the car in front of it has stopped, you can anticipate that and slow down. PAS will attempt to fill the gap in traffic by accelerating up to the next car in front of you, and then slow down only when necessary.

It did the above flawlessly, realized it had gotten itself into some trouble, and did a panic stop without hitting the car in front me. Unfortunately for the millennial in the SUV behind me, she was not using PAS (or paying attention) and rear ended me at 5 MPH.

Technically I could have mitigated this in two ways within the bounds of the Porsche system - first by restricting the top speed of the PAS to perhaps 25 MPH. Second, I could have lengthened the following distance, though that is problematic in traffic where cars are cutting into each other's lanes. Of course I could have just driven the damn car myself and this may not have happened.

I kind of wish I had just gotten the Sport Chrono package in hindsight. Until the sensor can see through the glass of the car in front of you and "paint" then track every car on the road as a human's eyes can, these systems are merely aids. I would include Tesla, Audi, Mercedes, BMW and everyone else in this generalization. I do leave the system partially engaged to get crash warnings, but find myself not using it unless for actual 75 MPH highway cruise.

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Thanks for posting. I use my ACC all the time, almost never in that sort of traffic, though. I love it on my commutes. And I do lengthen the distance when being tailgated. But I think you are right about the risk because it only watches one car ahead. I'll be quicker to brake manually in those cases in the future. Sorry you got hit; glad you're ok.

Edit: I did have the PAS alarm go off once just as I was hitting the brakes. Very glad to have it, even if the ACC has flaws.
 
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Thanks for posting. I use my ACC all the time, almost never in that sort of traffic, though. I love it on my commutes.
The technology really interests me. And as you mentioned, the PAS is valuable to me as well. I have to admit it is the existence of this feature that makes PDK appealing -- as weird as that sounds. I mean, I really lean towards the 6MT but if I choose the PDK in the configurator I immediately add the ACC/PAS.
 

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The technology really interests me. And as you mentioned, the PAS is valuable to me as well. I have to admit it is the existence of this feature that makes PDK appealing -- as weird as that sounds. I mean, I really lean towards the 6MT but if I choose the PDK in the configurator I immediately add the ACC/PAS.
Yes, for my use, the ACC is invaluable, and was the clincher on the PDK. I have come to love the PDK, though it's not perfect.
 

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I guess you can blame PAS for setting up that accident scenario. But it's still the fault of the driver behind you for following too close.

Too many inattentive drivers on the road. Whenever I hit the brakes, traffic jam or not, my first instinct is to check my 6. Almost every accident I've been in as a driver or a passenger, I've been rear ended.
 

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Yea, that was the first thing the SA warned me about with my first Porsche, "Remember the guy behind will not stop as fast as you do."
 

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Yea, that was the first thing the SA warned me about with my first Porsche, "Remember the guy behind will not stop as fast as you do."
Amen! I once got a tour of the Nummi factory, where they built small Toyotas. The rear drum brakes looked like tuna fish cans.
 

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I guess you can blame PAS for setting up that accident scenario. But it's still the fault of the driver behind you for following too close.

Too many inattentive drivers on the road. Whenever I hit the brakes, traffic jam or not, my first instinct is to check my 6. Almost every accident I've been in as a driver or a passenger, I've been rear ended.
Yes and no...

The OP post stayed on my mind all morning as I was driving to work in a heavily jammed traffic. I was testing the theory every time I braked in my SUV.

At first I was not convinced, as I was saying he's driving a Porsche which is very low to the ground. The driver behind could see the car in front no matter what as he'll be driving a higher car. So I thought it was fault of the driver behind until...

Until I got in sudden braking situation where as my car came close to stop I noticed the car behind me is still gonna hit me in the back so I eased on the brakes a bit giving it more space to stop. The three cars came to full stop safely but with very small gap in between with no accident, thank God. And that's when it hits me.

The PAS will not ease on the brakes or allow the driver to ease on the brakes to give more space to the car behind to prevent the accident, unless I'm wrong.

There's no system that's bulletproof, but I think the OP and my morning theoretical test proved one of its flaws.
 
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Yes and no...

The OP post stayed on my mind all morning as I was driving to work in a heavily jammed traffic. I was testing the theory every time I braked in my SUV.

At first I was not convinced, as I was saying he's driving a Porsche which is very low to the ground. The driver behind could see the car in front no matter what as he'll be driving a higher car. So I thought it was fault of the driver behind until...

Until I got in sudden braking situation where as my car came close to stop I noticed the car behind me is still gonna hit me in the back so I eased on the brakes a bit giving it more space to stop. The three cars came to full stop safely but with very small gap in between with no accident, thank God. And that's when it hits me.

The PAS will not ease on the brakes or allow the driver to ease on the brakes to give more space to the car behind to prevent the accident, unless I'm wrong.

There's no system that's bulletproof, but I think the OP and my morning theoretical test proved one of its flaws.
But mind the difference between PAS and ACC. I think the OP was really about ACC not PAS. PAS will mitigate a collision but not stop the Porsche in time to prevent it. You wouldn't want it to ease up. But what you wrote applies perfectly to ACC. ACC, when engaged, won't ease the brakes, BUT you can override it by turning off cruise control, or pressing on the gas, or swerving, or even braking yourself. Understandably hard to parse this stuff without the sort of detailed study of the manual one would only do if one's own car had it.
 

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Discussion Starter · #11 · (Edited)
I wasn't explicit but I did physically press the brake pedal. The cockpit made sounds like a stalled airplane to let me know it needed help. Maybe it would have stopped; maybe the braking force required was in excess of 0.35G and it needed me.

I wonder if it uses an accelerometer, or a fixed amount of braking force. In the latter case loaded vehicle weight, brake pad material, and coefficient of friction on the tires would make a difference in how quickly the computer could stop.


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I wasn't explicit but I did physically press the brake pedal. The cockpit made sounds like a stalled airplane to let me know it needed help. Maybe it would have stopped; maybe the braking force required was in excess of 0.35G and it needed me.

I wonder if it uses an accelerometer, or a fixed amount of braking force. In the latter case loaded vehicle weight, brake pad material, and coefficient of friction on the tires would make a difference in how quickly the computer could stop.


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Interesting, I didn't realize that. I've noticed that when I press the brakes when the ACC is already braking, the pedal feels different. The system is already pressurized and the pedal is high and firm.

There's a video out there somewhere by Consumer Reports, I think, using a big piece of cardboard? to simulate a vehicle that suddenly stops in front of a PAS-type car. The system brakes, but not enough to avoid the collision entirely.

So, you were using ACC, but got a PAS alert, too? And then you added more braking force to the default? Fascinating!
 

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There's a video out there somewhere by Consumer Reports, I think, using a big piece of cardboard? to simulate a vehicle that suddenly stops in front of a PAS-type car. The system brakes, but not enough to avoid the collision entirely.
I don't know how good Porsche's version is. You might be talking about this IIHS test. Subaru's version will stop the car. The difference is Porsche uses RADAR, the Subaru uses stereo cameras. The first gen was b&w, the second gen is in color.



 

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Not the video I saw, but still good.
 

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Until I got in sudden braking situation where as my car came close to stop I noticed the car behind me is still gonna hit me in the back so I eased on the brakes a bit giving it more space to stop.
And this is why I check my rear view mirror whenever I brake. So I can ease a little closer to the car in front of me if it looks like the car behind me is coming in hot.
 

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When I'm driving on the highway I spend more time driving the traffic behind me than the traffic in front, i.e. is that person going to pass on the inside? Are they too close to stop in time? Is there a faster car approaching? The people in front are pretty easy to deal with in comparison.

I'm not really a fan of these driver aids because there are already too many people out there that don't take driving seriously and give it sufficient attention that it feels like these aids are just helping them to not look or think about what they are doing. If you're a driver who takes pride in driving well then they can help you spot things you might have missed, but for many they're a sticking plaster for their lack of ability.
 

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Until I got in sudden braking situation where as my car came close to stop I noticed the car behind me is still gonna hit me in the back so I eased on the brakes a bit giving it more space to stop. The three cars came to full stop safely but with very small gap in between with no accident, thank God. And that's when it hits me.

The PAS will not ease on the brakes or allow the driver to ease on the brakes to give more space to the car behind to prevent the accident, unless I'm wrong.

.

It was my understanding of how the system works, that once the driver intercedes with either the brakes or the gas, that the ACC/PAS system is overridden, and at that point, the driver's input takes precedent? So, I assume you would still have the capability to "ease off on the braking"? Do any actual owners of an ACC/PAS equipped car know if this is true?
 
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