A DRIVERLESS car is not yet ready for the market. But in the meantime, automakers are continuing to market some components of one. The Ford Motor Company announced last month that it would offer “lane-keeping technology” as an option for its 2013 Ford Fusion and Ford Explorer. The price has not yet been set.

When lane-keeping technology works, it can save lives. But it is suited only for certain road conditions, and there are reasons to doubt that it will activate as consistently as it should.

Ford’s technology relies on a camera mounted to the rear-view mirror. When the system is switched on and the vehicle is traveling more than 40 miles per hour, it will use the road’s lane markings to sense veering near one edge of the lane or the other. If the turn signal is off, the system will assume that the drift is unintentional and will send a vibration to the steering wheel as a warning.

If the driver doesn’t correct the drift, the software is then supposed to engage the power steering and turn the car back toward the center of the lane.