Many automakers are offering some type of lane departure warning system, but the one on the 2010 Mercedes-Benz E-class and 2009 Mercedes-Benz S-class could be the best we've tested so far.
Instead of an annoying beep (like some systems use to get your attention), the Mercedes system vibrates the steering wheel if the car unintentionally leaves the lane. A small camera that resides near the rearview mirror can read the lane markings on the pavement, as well as the driver's actions, and distinguishes between a quick passing maneuver without a turn signal and a gentle departure from the lane (perhaps from looking at a passenger instead of the road ahead).
If the car determines the driver intended to leave the lane and is fully in control of the vehicle, there is no warning. When the system determines the lane departure is accidental, the steering wheel will vibrate. The camera can distinguish between solid and dotted lane markers and the warning is more aggressive if the car crosses a solid lane marker.
Our favorite part of the new system is the ability to detect when the lane departure is intentional, such as during aggressive cornering, quick passes, and when merging on a highway, and no alert is given. This type of tuning isn't done by some other manufacturers and the result is a very unobtrusive system during regular driving, but a credible alert when you need it.