Automated safety systems have become standard in many cars, but how much do they really help? According to one study, quite a bit — as long as they take decisions out of drivers' hands rather than trying to warn them of impending disaster. The Highway Loss Data Institute has published the results of a survey that compared the crash avoidance features of different brands of cars with the number of property damage liability claims that were filed for them (property damage liability claims cover crash damage to another vehicle, so while it's not a perfect metric, it doesn't count cases where the driver wasn't at fault.)

One of the features tested was a forward collision detector, which gauges whether a vehicle is in danger of rear-ending another car and either warns the driver or brakes automatically. In Mercedes and Acura cars, auto-braking systems reduced damage claims by about 14 percent. Similar systems offered by Mercedes and Volvo that had warnings but no auto-braking reduced claims as well, but not by as much. Volvo's auto-braking system was tested as well, but the results weren't statistically significant.Some warning systems may be seen as false alarms, researchers say

Adaptive headlights, which adjust automatically to help drivers see around curves at night, also turned out to reduce claims, although the study notes it's unclear exactly what situations they're most helpful in. But one of the biggest surprises was the failure of lane departure warnings, which alert the driver if the car drifts out of its lane. These systems, tested in Mercedes and Buick cars, didn't appear to reduce claims at all, and they may even increase them (though these increases weren't statistically significant.) Once again, it's not clear why this is happening: the researchers suggest it's because drifting off the road doesn't usually lead to a crash, leading drivers to regard the warnings as false alarms. Systems that would automatically keep cars in their lane, meanwhile, have yet to be tested.