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7 Series - F01 / F02 (2009 - current)
The new re-designed 7 series F01 / F02 leads off the BMW Fxx chassis code!

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Old 08-18-2009, 07:54 AM
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hayden hayden is offline
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Join Date: Jun 2006
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Mein Auto: 2009 F02 750Li
Article: Stop-and-Go Active Cruise Control

http://www.gearlog.com/2009/08/hands..._active_cr.php



I hit the brake pedal just once on a 200-mile stretch of Interstate highway coming back from the Adirondacks to the New York City area. It wasn't while driving in the middle of the night but on a busy Sunday afternoon, when traffic can be bumper to bumper the last 50 miles. The car was under the guidance of radar-based stop-and-go active cruise control (ACC), also known as adaptive cruise control, autonomous cruise control, or intelligent cruise control. ACC has been around for a decade and recently some automakers have added a second radar transponder that covers near distances (sort of like radar reading glasses). Instead of cutting out around 20 mph, this takes you down to a full stop and back up to speed. Stop and go ACC is effective, but it's not cheap: It added $2,400 list to the price of the BMW 750Li I was driving, which in turn helped hike the price over $100,000. But it's effortless: The only driver involvement, other than steering (still highly recommended), is to lightly tap the throttle when you're stopped and ready to start up again.

With active cruise control, just as with regular cruise control, you set the speed you want. A radar transponder (typically) or laser (some cars) in the front grille or bumper watches for moving vehicles directly ahead, locks onto them, and maintains a safe or really-safe following distance. The driver can always override ACC with the throttle or brakes. ACC is excellent at locking into the vehicle in your lane, not an adjacent lane. For most of my most recent journey, active cruise control worked fabulously well, as it has on other vehicles on previous drives. It tracked reliably around the gentle curves of a limited-access highway but can lose a vehicle on a twisty back road or going around a sharply curved exit ramp, when you really shouldn't be using ACC anyway. If you shift lanes to get out from behind a slowpoke and there's a big difference between the ACC speed setting and your current speed, the car may surge ahead (this BMW had 400 hp and two turbochargers under the hood). If you shift lanes and there's another car ahead in the new lane, it takes a moment to lock on while you're accelerating ahead, sometimes to the consternation of the passengers in your car. If a slower-moving car cuts in front of you, it will take a moment to lock on and adjust your speed.

The one time I hit the brakes, it was to avoid an impending accident: A slow-moving truck swerved out of its lane into mine. With concrete construction barricades closing off the breakdown lane, there was no place open except behind me. The orange radar-lock icon turned to red (indicating a potential crash situation where the car may not be able to slow down enough to avoid a collision) and a loud alert sounded, but by that time I was already hard on the brakes. We quickly were out of harm's way.

Active cruise control lets you set three, sometimes four, following distances. Usually you choose the farthest-distance setting when traffic is light, the shortest distance (see inset in photo) in heavy traffic in New York or California where other drivers would dive into the space in front if you give them half a chance. Sometimes even the shortest distance isn't short enough and you get pushed back when another car wedges into the opening ahead of you.

Active cruise control is often paired with an imminent-collision warning system, which means the ACC thinks it can't stop in time but the driver possibly can by hitting the brakes, and with collision mitigation, meaning the car will slow enough that if there is an accident, that it's at a lower speed. That's because ACC braking is by design never as vigorous as the driver can apply by standing hard on the brakes. ACC also can't deal with stationary objects, for instance if someone built a brick wall in the middle of the road, or if a car stalled on the highway on a foggy night. Those exceptions, while scary, are few and far between.

If you tap the brakes, even gently, ACC disables and you're pretty much on your own. I've found myself wishing the car would continue to keep active at least the braking part of ACC because sometimes in heavy traffic it's hard to remember if you touched the brakes. So, when the distance to the car in front starts to get uncomfortably close, you're unsure if ACC is active or not. Don't be silly, the automakers tell me: Just glance down at the instrument panel to see if the ACC-active light is on. Silly me: I've found the last thing I want to do is look down in heavy traffic. And yet I don't want to hit the brakes if ACC is active because I know ACC then will be deactivated. If you haven't driven ACC cars, it may sound as if the driver is too stupid to know if he was on the brakes and too lazy to hit the brakes. It's something that could be improved in ways that don't take any more control away from the driver. Perhaps the driver has an option to keep ACC braking active after light pedal presses but not after heavy braking, and if that's the case, the ACC indicator says ACC Off rather than disappears from the instrument panel display, or there's a falling-pitch sound that suggests a device was powered down.

ACC cars without the stop and go feature cut out at 20 mph to 35 mph: A tone sounds, a light flashes, and you're on your own. With or without ACC, current Volvos include a City Safety feature that automatically stops the car below 19 mph (30 kph).

More than a dozen automakers in the U.S. offer active cruise control. Most systems run $2,000 and up, which means 2% of the price of a $100,000 car (essentially a rounding error) or 10% of the price of a $20,000 car, which is why you mostly see it on $40,000-plus cars. Lexus charges most, $2,895, for radar cruise control with a pre-collison warning system. Audi gets $2,100. American automakers typically charge less. Cadillac charges $1,695. Ford's active cruise control is pushing ACC prices down toward $1,000 for radar-based systems; it's $1,195 on the 2010 Ford Taurus. Chrysler has an older laser-based system on the 300C that's $695.

Automakers with active cruise control on one or more models, not all of them offering it in the U.S., include:
Acura
Audi
BMW
Cadillac
Chrysler
Ford
Honda
Hyundai
Infiniti
Jaguar
Lexus
Lincoln
Nissan
Mercedes-Benz
Range Rover
Renault
Subaru
Toyota
Volkswagen
Volvo
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ED Vehicle: 2009 F02 750Li | Black Sapphire Metallic | Black Nappa Leather | Fineline Matte Wood Trim
ED Tour: Aug 25th - Sep 9th 2009. (Itinerary | Trip Report | Route Map).
ED Progress: Welt Delivery Aug 27th; Drop off at Paris Sep 8th; Redelivery October 30th.

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