lane departure systems

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Technology Guide: What Are Lane Departure Systems, and How Do They Work?

The modern highway is a blend of sight and sound, composed of texts, tunes, GPS navigation systems, headlamps, and more. No wonder that distracted and drowsy driving are on the rise.

According to the National Highway Traffic Safety Administration (NHTSA), run-off-road accidents comprise 70 percent of fatal single-vehicle crashes, even though they are a small fraction of total automobile accidents. The NHTSA identifies night-shift workers and young males as most prone to drowsy driving, and in some states, 25 percent or more of automobile collisions are due to distracted drivers.

The automotive industry intends to reverse this disturbing trend with lane-departure warning systems (LDWs).

What are Lane Departure Systems?

A lane-departure warning system is a mechanism that alerts a driver when his or her automobile begins to veer out of its lane without the turn signal engaged. Lane-departure warning systems are not the same as lane-keeping systems (LKS), which can urge the vehicle back on course.

How Do They Work?

The heart of an LDW system is its eye: a camera, laser sensors, or infrared sensors. Video cameras peer out from the middle of the vehicle and are often integrated into the backside of the rearview mirror. Infrared and laser sensors can be attached to the windshield, the front, the rear, or even underneath. Most monitor the road ahead, a few watch the road behind.

Visual processing software parses the video feed, looking for road surface markings, such as the white or yellow solid or dashed lines marking the borders of a lane. By using trigonometry to calculate the distance between lane borders, the LDW system knows when a vehicle is properly centered.

When a car begins to drift out of its lane, the lane-departure warning system will issue an alert. It cautions the driver to return the car to the center of its lane. Properly responding to an alert requires awareness of the surrounding traffic environment. LDW systems cannot fully compensate for the driver.

Most systems beep until the driver returns the vehicle to the center of the lane. Some technologies vibrate the steering wheel or the driver’s seat cushion, and a few flicker a light onto the dashboard.

If a turn signal is engaged, an LDW system does not provide a warning signal.

Unlike Lane Departure Warning systems, Lane-keeping mechanisms do more than just telegraph alerts. They can automatically steer the automobile back to the center of the lane. A driver may, at any time, easily override the system by turning the steering wheel.

How Do Drivers Use Them?


Original equipment manufacturer (OEM) lane-assist systems are integrated into the vehicle’s electronics. Most activate by default. They can be deactivated by pushing a button or accessing controls through a touchscreen interface. Once deactivated, some systems hibernate until they are manually recalled, while others restart after every ignition. If a driver forgets to turn off the turn signal after switching lanes, the LDW system will remain inactive.

The Effectiveness of Lane-Departure Warning Systems

In the decade or so since LDW systems were first implemented, users have reported increased confidence and decreased wrecks. Yet LDW systems are not miracles. They are mechanisms. On the snow-covered roads of Michigan’s Upper Peninsula, they cannot see lane markings. On the antique asphalt of Appalachia, the system cannot discern faded borders. On such roads, it may give false alarms, and it may even fail to notice drifts and yaw. In such circumstances – in fact, in all motoring circumstances – drivers should rely first and foremost on their own foresight and mindfulness.

Although LDW systems work on curved roads, they are designed for highways. Most do not function below 30-35 mph or in metropolitan areas.

The Honda LaneWatch (TM) System


Perhaps the loudest critique leveled at lane-departure systems is their ruthlessly rational autonomy. They can be insistent and easily confused, incessantly beeping without obvious reason. Honda has adopted a unique strategy to overcome this Achilles’ heel: the Honda LaneWatch.

It preserves driver’s responsibility while adding an extra layer of protection. The way it works is that a small camera is attached to the underside of the passenger-side rearview mirror. It provides four times the sight as a standard exterior mirror, expanding the field of view from 20 degrees to 80 degrees. The camera feeds video into the car’s 8-inch display screen, and it imposes red and yellow reference lines onto the image to help drivers gauge distances.

LaneWatch activates automatically when the right turn signal is engaged or when the lever button is pressed. The driver can also activate the camera during straight line driving. With LaneWatch, all vehicles, cyclists, and bikers on the passenger side can be clearly seen.

With LaneWatch, drivers cannot push responsibility onto a computer. Rather, the system empowers drivers with a superior field of view and an enlarged color picture. For such creativity, Good Housekeeping awarded LaneWatch with a 2013 Very Innovative Product Award. AOL Autos named it a 2012 Technology of the Year Finalist.

Honda offers LaneWatch across the lineup on the Odyssey minivan, Accord Sedan, Accord Coupe, and upper models of the Civic Sedan, Civic Coupe, and Fit hatchback.

Lane-departure warning systems provide a “third eye” that protects passengers and exposes blind spots. Honda LaneWatch does the same, but it leaves the power of driving where it belongs: in human hands.

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