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Lane Departure Warning System
What Is It?
Lane Departure Warning (LDW) systems alert you whenever you unintentionally drift too close to the edges of the lane. The warning type varies between car manufacturers; some use an alarm sound, while others cause the driver’s steering wheel or seat to vibrate, creating a feeling like driving over a rumble strip.
LDW systems should not be confused with Lane Departure Prevention systems (sometimes referred to as lane keeping assistance). Warning systems provide a warning, but leave any corrective actions up to the driver. Prevention systems gently steer the car to automatically re-center it in the lane.
Why Did LDW Earn a 3-Open and 1-Solid Star Rating for Lane Departure Scenarios?
LDW has been estimated to have the potential to reduce fatalities in lane departure-associated head-on crashes by as much as 46% (3 open stars). However, objective real-world data is very limited, and a study of one specific system pegged the reduction in certain crashes at 1-8%. So, the proven, solid star rating stands at 1.
Why did LDW Earn a 3-Open and 1-Solid Star Overall Safety Benefit Rating?
When factoring in lane-departure prevalence among all crash types, theoretical overall reductions of 3%, 5.4%, and 23%, respectively, have been estimated for crashes, injury crashes, and fatal crashes (3 open stars). However, despite a relatively high potential, limited real-world data exist to document a proven benefit. As such, LDW has only earned 1 solid star to-date.
Why Would I Use This Technology?
Lane departure crashes are one of the most common crash types, accounting for 1.6 million road collisions per year. The primary benefit of this technology is that it alerts the driver in an effort to prevent such crashes.
What Do Drivers Think?
Studies that gave drivers a LDW system to try found that 85% of drivers reported liking the system and found it to be useful. 93% used the system at least sometimes, 77% felt it increased their safety, and 80% would buy the system again; 67% of drivers felt that LDW made them safer drivers.
How Well Does It Work?
LDW systems have been shown to improve lane-keeping by up to 34%, and in one study cut unintentional lane crossing in half. Drivers who used LDW systems also became more likely to use their turn signals, especially if they drove often on highways. Some in the driving safety research community have questioned the extent to which motorists actually turn off the warnings while driving, and thus would be unable to benefit from the system. A need for additional research into how drivers interact with such systems and specific implementations of warning systems has been suggested.
Who Benefits Most?
LDW systems are most useful to drivers who often drive on highways and rural roadways. Some research suggests that the systems may provide greater benefit to younger drivers. LDW is less helpful for city drivers.
In What Situations Doesn’t It Work?
LDW systems work by “looking” at the road’s lane markings. These systems are less accurate on roads where lane markings have faded or are in poor condition, or in cases where bad weather (such as snow) obscures the markings. They are also somewhat less accurate at night or other low-light situations. These systems are better suited to highway driving, and will be less useful in cities.
LDW systems may increase driver confidence, and also help drivers realize when they may not be paying sufficient attention to the roadway.
Not All Systems Are Alike
Some manufacturers put the LDW system on by default, while others leave it off by default. Remember, you won’t benefit from the system if it’s not turned on, so check your car’s manual to be sure you know how the LDW system is activated and are aware of any conditions that will impact its function. Some LDW systems use an alarm sound, while others make the steering wheel or seat vibrate, similar to the feeling of a rumble strip.
Different Names, Same Idea
A variety of different terms may be used to descibe LDW systems, so it is important to ensure you are clear on the distinction between LDW systems and those designed to provide more active assistance. As noted earlier, LDW systems are conceptually different from lane keeping assistance systems that intervene in vehicle steering to aid in keeping your vehicle within lane boundaries. The latter technologies are often identified by terms such as “lane keeping assistance” and “lane keeping support."
How Can I Learn More?
Full references to all studies quoted above can be found in the official AAA Foundation report, "Evaluating Technologies Relevant to the Enhancement of Driver Safety." The project's Fact Sheet provides more detail on the rating system itself, and the criteria used to assign solid and open stars, both for Overall and Scenario Specific ratings.