(Volvo Cars of North America)

The number of ways driver error can cause traffic accidents is practically without limit, but lane departure warning and lane keep assist systems seek to reduce that number by mitigating the effects of driver fatigue, inattention, or plain-old brain cramps.

Here’s how it happens: You’re cruising along the freeway normally, and maybe you’re fiddling with the infotainment system, talking to someone, or just zoning out. Your vehicle begins to drift out of its lane, and because you haven’t signaled a turn, your vehicle interprets this as an unintentional maneuver. If you have a lane departure warning system, that system will set off some bells and whistles, or blinking red lights, or whatever else the manufacturer decided would best alert the driver to their mistake. If you have a lane keep assist system, your car will take it one step further. Not only will it alert you to your mistake, but it will automatically correct it to keep you in your lane.

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Mitsubishi debuted this technology in 1992 on the Debonair (which was only sold in Japan), and by the early 2000s some version of it or another was popping up across the automotive world. The technology relies on video, laser, and infrared sensors, commonly mounted on the back of the rearview mirror, to determine which lane the driver has chosen.

As noted, the turn signal is a key cog in this operation. It used to exist purely to alert other drivers of your intentions, but with these systems in place, it fulfills the essential duty of letting your car know what your plan is, too. What this means, in practical terms, is that if you don’t want your car hollering at you about your lane changes, you’re going to have to signal every one of them. These systems can be turned on and off, for those times when the driver would rather carry on unassisted.

And that’s exactly what happens in the real world, about two-thirds of the time, according to the Insurance Institute for Highway Safety. Further, there are some doubts as to whether these systems are actually preventing crashes.

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“The findings are consistent with previous research showing that vehicle owners found lane departure warning more annoying than other crash avoidance technologies,” the IIHS reported last year.

Ten years after the technology debuted in the United States, the IIHS couldn’t tell whether or not it was having any effect.

“The jury is still out on these systems,” IIHS spokesman Russ Raider told Boston.com in 2015. “But so far we don’t see any evidence they are working to prevent crashes.”

Lane departure warning and lane keep assist are now ubiquitous options on cars sold in the United States, and come standard on some luxury vehicles. The sensory technology is part of the underlying framework of autonomous driving technology, so these systems aren’t likely to go away any time soon, even though most consumers could take them or leave them.