Tesla promises full self-driving cars by year end, but regulators are wary.

Once the update arrives, Tesla vehicles will be able to drive themselves in a city the way they can perform highway cruising now, the company said. That means interpreting stop signs and traffic lights, making sharp turns, and navigating stop-and-go urban traffic and other obstacles -- a far more difficult task than navigating long, relatively straight stretches of highways. Although Tesla's website has promised features as soon as this year including the ability to recognize and react to traffic lights and stop signs, and what it calls "Automatic driving on city streets," the suite would still require a human driver behind the wheel. As soon as next year, Tesla has said, the cars will be able to operate reliably on their own, even allowing the driver to fall asleep. This tiered approach is different from companies such as Waymo, whose sole aim is to launch autonomous vehicles that do not need a driver behind the wheel.