How does Lane Departure Warning work?

I’m in the process of buying my dad a new Honda CRV which will probably be his last car. I’m impressed with the optional safety features and was explaining some of them to him. Can you shed some light on the lane departure feature, or is it lane-keeping — how it works? He’s resistant to technology but I’m trying to keep him as safe as possible. I’m curious also how some of the technical aspects of this might work as well. — Julian F. Sunnyvale CA

This is cool technology that is becoming common on many vehicles. Lane Departure Warning (LDW) is a system that employs a forward looking camera (s) into a small module above/behind the rear view mirror. The builtin brain uses object and pattern recognition software to interpret the roadway stripes and curbs to see if the vehicle is staying within its lane. If the driver uses the turn signal or rotates the steering wheel (steering torque and angle sensors verify this) the system assumes the driver has a purpose in deviating from the lane and stands down. If the vehicle drifts away from the lane center significantly with no driver inputs, an audible and visual alarm typically warns of needed correction. Some vehicles may also vibrate the steering wheel or speak to you to summon attention. Honda’s system must be turned on/active with each drive (Dad may not want to or remember to do this!) and works between 40-90 mph.

Lane Keeping Assist Systems (LKAS) take this one step further by using the electric power steering system and in some cases one or more brakes to gently nudge the vehicle back towards its lane. The driver needs to take over and supply the steering movement to complete the correction. The stability control system, looking at vehicle speed, steering angle, and vehicle yaw rate stands by if need be to mitigate any over-correction. Some vehicles take things even further using lasers, radar, GPS technology, mapping, and accumulated vehicle tracking information to know exactly what’s ahead.

LKAS may work in harmony with adaptive cruise control, and provides the building blocks for autonomous vehicle operation. I’m impressed with how many vehicle control modules are involved and how an enormous amount of data must be rapidly shot back and forth to make this all work in real time.

LDW and LKAS are generally not active when the windshield wipers are in use, foggy weather or dirt obscures camera vision, the road contains broken or faded stripes, or the road has sharp turns. I’ve driven a few vehicles equipped with this and found the sensitivity and corrective actions can vary quite a bit depending on the manufacturer and certain road conditions. Some folks report LKAS can be annoying due to false alarms and excessive steering wheel correction.

Brad Bergholdt is an automotive technology instructor at Evergreen Valley College in San Jose, California. Readers may send him email at bradbergholdt@gmail.com; he cannot make personal replies.