You can drive hands-free with your next car. Is that a good thing?

Car companies have added safety technologies to prevent accidents, such as automatic emergency braking and systems to prevent the car from deviating from its lane. Now more vehicles are introduced that should make driving in rush hour traffic or on car journeys less stressful.

Some new systems allow drivers to keep their hands off the wheel on highways or in heavy traffic jams, using sensors, radar and cameras to automatically keep the car centered, control speed and even change lanes.

General engines Co.

was the first major auto company to promote such capabilities in 2017 with its hands-free Super Cruise function, which can be activated on most US highways by pressing a button on the steering wheel that allows the car to take over steering and speed control.

The Detroit automaker said it now plans to roll out the technology on about two dozen models by 2023, compared to one Cadillac model now.

Ford Motor Co.

F. -1.45%

recently said it would offer similar technology on as many as 100,000 F-150 pickup trucks and Mustang Mach-E electric sport utility models starting next year.

Honda Motor Co.

HMC -0.45%

plans to roll out a sedan in Japan in the coming months that will allow the driver to completely relinquish control of the car in heavy traffic or on highways. The technology even allows drivers to keep their eyes off the road, although they are expected to take control at any time, the company said. The Japanese government regulators approved its use in November.

Honda said it has not revealed any plans to introduce this technology outside of Japan.

Meanwhile, Tesla Inc.

TSLA 2.44%

said it recently released a test version to some owners of its improved Autopilot, the automaker’s driver assistance feature.

The $ 10,000 feature, which the company calls Full Self Driving, extends the use of automated functions to more types of roads and adds capabilities such as navigating highway junctions.

The promise of fully self-driving cars has faded in recent years as developers struggle to refine the technology. But automakers are equipping more models with the building blocks of self-driving cars to offer so-called driver assistance packages, in the hope of gaining a competitive advantage and boosting sales.

“They allow car manufacturers to offer really interesting, differentiated functions to consumers at a reasonable price,” said Glen De Vos, Chief Technology Officer of Aptiv PLC, a supplier of software and components used in driver assistance systems.

Consumer Reports recently tested 17 models that combine automatic steering and speed control, up from four when the magazine ran a similar test two years ago. The magazine said such systems can reduce driver fatigue, but performance varies widely on aspects such as how smoothly they brake and accelerate or keep a car in the middle of the lane.

But when drivers have less to do behind the wheel, safety attorneys are concerned they will be tempted to look at their phones or indulge in other distractions, which could lead to accidents.

“If we’re going to apply this technology to cars, we need to make sure that the driver is reasonably involved,” said Bryan Reimer, a researcher at MIT who studies driver assistance systems.

Some advocates have criticized Tesla for promoting the latest update as self-driving for not being fully autonomous, and advocates say a trial system should not be tested on public roads.

Tesla did not respond to requests for comment. The electric vehicle manufacturer has previously said that accident rates are lower when drivers have vehicles with the Autopilot steering assist system engaged than when it is not in use.

Car manufacturers have installed camera-based systems that monitor drivers’ focus and alert them if their attention drifts, executives and analysts say. GM and BMW AG

BMW 1.78%

use the technology to keep drivers engaged, and Ford and others plan to use it in future models. Such systems have received praise from researchers.

Aptiv’s Mr. De Vos said the company is working with five automakers to equip vehicles with camera-based driver tracking systems.

Cadillac owners have covered about 6.5 million hands-free miles using the Super Cruise technology, the company said. A series of audible warnings alert drivers if their attention strays from the road.

Mario Maiorana, chief engineer of GM’s Super Cruise, said it has become a selling point for customers, noting that 85% of owners say the feature would be an important consideration in their next car purchase.

“People have told us that they feel like they arrive at their destination refreshed and relaxed because of the work we’ve done,” he said.

A recent update improved driver monitoring technology, he said. It can now track the driver’s eyes, rather than just the position of the head, to better detect whether the driver is stuck on the road or elsewhere.

A bill from the U.S. Senate introduced this year would require the U.S. Department of Transportation to investigate whether driver tracking systems could reduce distracted driving, and that this may be required for future models. The legislation, introduced in July by Edward Markey (D., Mass.) And Richard Blumenthal (D., Conn.), Is pending.

A spokesperson for the department’s National Highway Traffic Safety Administration said it is investigating whether driver monitoring systems are effective in identifying and reducing inattentive or disabled drivers.

The growing availability of driver assistance systems has resulted in a mish-mash of different features that vary by model and car manufacturer, said Kelly Funkhouser, a vehicle test manager who leads automated vehicle coverage at Consumer Reports.

“These systems all behave so differently and there are no standards for performance or design,” she said. “There must be more cohesion.”

Write to Mike Colias at [email protected]