
Our XC60 is fitted with Volvo's Collision Warning system which flashes a visual alert on the windshield, triggers an audio alarm and will apply the brakes at up to 50 percent of maximum braking power. I had a few false alarms from this system when driving the XC60 over the weekend. One is excusable, the other might not be.
The above photo shows the visual alert which is a line of LEDs built into the dashboard that reflect off the windshield when illuminated. They're much brighter and more obvious than this photo illustrates.
Here are the two scenarios:
The first false happened leaving our office's underground parking garage last week. When approaching the ramp, the system activated in all it's beeping, flashing glory. The ramp to street level is steeply raked enough that it's likely the rear-view-mirror-mounted laser sensor saw the it as an obstacle directly in the line of travel. Because there was no risk, I kept my foot in the throttle and the brakes were never applied -- but the warnings were distracting.
The second situation is less easily forgiven. The system was triggered when driving down a narrow, curving two-lane street at 25 or 30 mph in moderate rain. My guess is that the sensor probably picked up one of the cars parked on the side of this very narrow street and assumed (because the street curves heavily) that it was a car in my lane. In some places on this street parked vehicles actually align directly with the front of cars driving in the lanes. Again, the audible and visual warnings only last a few seconds and the brakes were never applied.
Systems like Collision Warning and City Safety (which can completely halt the XC60 at maximum brake force) are substantial pieces of technology which utilize expensive hardware and demand extensive tuning. Having the sensor range necessary to make them effective probably requires compromises like these in certain situations. Whether those compromises are worth it or not is up to you.
Josh Jacquot, Senior road test editor

stephen987 says:
04:45 PM, 12/ 7/09
I don't want it. But I wouldn't mind if the idiot talking on his cell phone has it.
cr_driver says:
06:00 PM, 12/ 7/09
Exactly stephen.
clarkma5 says:
06:02 PM, 12/ 7/09
I would pay to not have systems like these in my car.
stwok says:
06:51 PM, 12/ 7/09
great post.
vt8919 says:
07:22 PM, 12/ 7/09
So how'd you get the system to activate in the picture?
greenpony says:
07:40 PM, 12/ 7/09
I guess they need sensors for speed and steering angle to make the system "smarter".
billt9 says:
11:00 PM, 12/ 7/09
greenpony,
That wouldn't help, as the above described scenarios actually do have obstacles directly in front of the vehicle. It just couldn't tell if:
1. The vehicle is capable of climbing over the obstacle (scen #1)
Or
2. If the driver intends to turn once getting close to the obstable (scen #2).
All cars these days have speed and steer angle sensors, as used in stability control.
jsc4321 says:
12:49 AM, 12/ 8/09
wait...these systems are all optional right?
mrryte says:
06:44 AM, 12/ 8/09
stephen987 says:
I don't want it. But I wouldn't mind if the idiot talking on his cell phone has it.
Which it PRECISELY why they made it-to protect pedestrians and other drivers from the stupidity of inattentive drivers. ;-)
creeper says:
07:01 AM, 12/ 8/09
vt8919-
evidently by still going 35 mph while approaching a stoplight 75 feet away and taking a picture with a cell phone.
milt721 says:
08:52 AM, 12/ 8/09
What is the warning on the nav screen? From what I can make out, it looks like the system knows its raining...
benson2175 says:
09:05 AM, 12/ 8/09
A friend's dad owns an S Class and he's had the system activate while driving. It closed the sunroof and rolled up the windows and apparently tried to choke him with the seat belt. I don't know the details of where he was driving at the time but he wasn't close to crashing into anything.
mercedesfan says:
01:39 PM, 12/ 8/09
@benson2175,
Well he must have been doing some crazy stuff. The only reason the moonroof would close would be if the car sensed it was rolling over (a frontal collision doesn't trigger that aspect of the system). The likelihood of a rollover is determined by pitch and roll sensors in the stability control system, not by the radar sensors at the front of the car that determine impact. Whatever he was doing was by no means normal driving.
I too have pushed my car a touch past sanity, but it has never mistaken that for a rollover.