Even as automakers introduce technology that lets cars drive themselves in congested highway traffic, their engineers and suppliers already are working on the next steps, such as automatic passing and lane changing.

Those next steps would allow some drivers to sit back and let the car do much of the work on their daily commutes, possibly around the end of this decade.

Fully autonomous cars -- the kind that would travel to a selected destination while its occupant takes a nap, reads a book or watches a movie -- are probably at least a decade away.

But vehicles that can take over for the driver at low speeds on limited-access highways already are on the way in Europe, including the BMW X5, Mercedes-Benz S class and Audi A8. They use sensors to maintain a uniform distance from the car ahead of them and to stay centered in a lane.

Mercedes-Benz calls the feature Traffic Jam Assist, while BMW and Audi use the name Traffic Jam Assistant.

As that technology becomes less expensive and more common, automakers are expected to work on making it work at higher speeds and adding the ability for cars to change lanes and pass slower vehicles.

Drivers ultimately would be able to relax and let their attention drift a bit more from the road, though the vehicle still could require them to take control at certain points, with a few seconds' warning.

"It's not really too much of a stretch from where these Traffic Jam Assist systems are today," said Andy Whydell, the head of product planning for TRW Automotive's global electronics business.