What the changes will mean to the century-old American romance with the car remains to be seen. But the safety systems, the result of rapid advances in computer algorithms and the drastically falling cost of sensors, are a practical reaction to the modern reality of drivers who would rather talk on the phone and send text messages than concentrate on the road ahead and drive.

Four manufacturers — Volvo, BMW, Audi and Mercedes — have announced that as soon as this year they will begin offering models that will come with sensors and software to allow the car to drive itself in heavy traffic at speeds up to 37 miles per hour. The systems, known as Traffic Jam Assist, will follow the car ahead and automatically slow down and speed up as needed, handling both braking and steering.

At faster speeds, Cadillac’s Super Cruise system is intended to automate freeway driving by keeping the car within a lane and adjusting speed to other traffic. The company has not said when it will add the system to its cars.

Already actions like steering, braking and accelerating are increasingly handled by computer software rather than the driver.

“People don’t realize that when you step on antilock brakes it’s simply a suggestion for the car to stop,” said Clifford Nass, a director at the Center for Automotive Research at Stanford. How and when the car stops is left to the system.

The automobile industry has been motivated to innovate by growing evidence that existing technologies like the antilocking braking systems and electronic stability control have saved tens of thousands of lives.

In November, the National Transportation Safety Board recommended that all new cars be equipped with collision avoidance technologies, including adaptive cruise control and automatic braking. Two states — California and Nevada — have passed laws making it legal to operate self-driving cars as long as a human being is inside, able to take over.