Unintended Lane Change

It happens all too often. A vehicle lunges across the centerline directly into the path of on-coming traffic. A head-on accident often results, and with it very frequently comes death.

The reasons for inadvertent lane-changes are many -- distractions caused by cellular phones, unruly children, substance abuse, lack of sleep, or even simple daydreaming. But no matter what the reason, the result is often the same -- a crunchingly harsh high-speed crash. Anything that distracts drivers from their main objective, which of course is to arrive safely at their destination, can be a sudden killer. Perhaps you've experienced this yourself; maybe you wanted to change CDs, turn on the heater or write a quick note. You took your eyes off the road for a split second and when you looked up your vehicle was lurching out of its lane. If you survived to tell about it, you are lucky, because many don't.

These days a common approach to preventing inappropriate or unintended lane departure is the use of "rumble strips" -- grooved pavement markings that alert the driver by causing a loud noise and vibration when the vehicle leaves its lane. But "rumble strips" have two crucial limitations. First, they only warn the driver after he has departed the lane, so in many situations, this kind of warning comes too late, and the driver is not able to recover vehicle control. And more important, rumble strips are only installed on a tiny fraction of our total roadway mileage.

To address the frightening results of unintended lane departures, Volvo Car Corporation, long known for its safety innovations, has unveiled an active safety system designed to prevent them. The system was just shown at the SAE 2003 World Congress, which took place earlier this month in Detroit.

The system uses an ingenious combination of existing technology. The Volvo Lane Departure Module uses a camera with image processing software to detect current lane position. A computer associated with the camera constantly measures distances from the camera's centerline to the left and right lane markings and can detect variations almost instantaneously.

If a driver mismanages steering control through inattention, the camera/computer combination determines the situation almost immediately and applies torque to the steering wheel designed to guide the driver back to the appropriate steering wheel angle required to come back in the lane. The system does not assume steering control of the vehicle but instead gives the driver a gentle nudge that will reactivate his attention in time to avoid leaving the lane in which he's traveling.

"Results from test drives indicate that, despite its simplicity, the system is fully sufficient for helping drivers stay in the lane without being perceived as an autopilot," said Jochen Pohl, an engineer at Volvo and an author of the SAE technical paper.

Volvo is not ready to introduce the system on its passenger cars, believing more work is to be done. Company engineers say the system function has to be "transparent" and understandable to the driver, and there must be a distinct distribution of responsibility between the driver and the system. The goal of the exercise is not to design an autopilot system that will steer the vehicle. Instead, the goal is to design a warning system that can aid the driver in reacting quickly to an inadvertent lane change before it occurs. And that can save lives.


Driving Today Managing Editor Jack R. Nerad is one of the few drivers who actually signals before making a lane-change. Most of the time, he is aware of what he's doing.