Quote:
Originally Posted by Qsilver7
In regards to when are brakes applied...really depends on what model year you have, how the car is optioned, and how fast you're going.
As the technology advanced from Driver's Assistance to Driver's Assistance Plus...more features were added...as well as the button to activate/deactivate stuff.
My suggestion is to "pay attention" and if you get the little "red car" warning...take immediate action to back down/slow down...and if you get the audible alert...start braking ASAP. Your brakes will be "pre-conditioned" at that point...but don't depend on the car to brake for you. If it does brake due to your inattentiveness or recklessness of the other driver...then consider yourself one lucky SOB. 
Here's a video that covers the multiple set-ups (camera and radar):
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correct. The red car icon is really just a driver's aid. There are multiple "sensitivity" settings to it. In a nutshell it calculates your speed versus the approach speed of the obstacle/car on front of you. It's constantly using ultrasonic sensors to detect and calculate it and factors in environmental variables (buildings, trees, rain, parked cars).
I have mine on the most sensitive setting. The red icon has come up numerous times when my approach speed on the highway to another car is way too fast. The most useful is when there's a major slow down on the highway, or a really slow car in the lane which happens often here in California. (not a false positive).
It comes on more often as a false positive. It happened once in my garage when it detected I drove into it way too "fast" and actually applied the brake a fraction of a second before I actually hit the brake (I knew what I was doing!). The most common false positive is a particular stretch of city road where it's a long fast sweeper and the driving lane is very close to parked cars on the road. As the road sweeps and the angle of the turn tightens, the sensor is close enough to think the parked cars on front has stopped. The icon comes on, but it's never hit the brakes for me before, likely because it's using some type of algorithm to factor in the fact I haven't hit anything yet for a "low probability" obstacle. (If you're in SF and want to test it, it's the west bound road at 702 Brotherhood Way, or you can google the street view to see what I'm talking about).
https://www.google.com/maps/@37.7144...7i16384!8i8192
BTW the BMW's ultrasonic system isn't very sophisticated. It's essentially a sonar type system. The current autopilot soft wares in the cars being tested utilizes combos of sound, radar and laser can be very accurate.