WASHINGTON — As I merged onto the freeway, a green strip of lights on the top of the steering wheel illuminated. My moment of truth had arrived.

I let go of the wheel and took my foot off the accelerator.

The car, a 2018 Cadillac CT6 sedan, began driving itself.

In a test drive of the new partially self-driving car technology offered by General Motors, I zipped around the Washington, D.C., area for about an hour Monday, often allowing the car to drive itself on the freeway for minutes at a time.

It was briefly unnerving, but jitters quickly gave way to trust as the car stayed safely centered in its lane, alternately braking and accelerating like a professional driver.

The technology, dubbed Super Cruise, which starts shipping to dealerships this week on premium versions of the CT6, worked precisely as described.

The technology allows you to take your hands off the wheel and feet off the accelerator and brakes. It works only on highways or freeways with ramp access, not in city driving, which is harder for self-driving cars.

Super Cruise is an interim step toward full autonomous driving. For now, it’s state of the art, providing a capability similar to Tesla’s Autopilot system, which also requires that the driver stay alert and occasionally take part in guiding the car. It also adds a new safety feature that federal regulators want automakers to embrace as an extra layer of protection.

Super Cruise hits the road as GM races against other automakers to develop full self-driving vehicle technology.

The ultimate goal is a car in which drivers don't drive, but rather sit back as they are whisked to their destination. GM is developing such a system for the Chevrolet Bolt, its new long-range electric car model. But it could take several years before that technology is available to the public.

The Super Cruise package, which includes adaptive cruise control, is a $5,000 option on the CT6. The CT6 Platinum comes with it standard at a base price of $85,290.

It works like this:

Once you’re centered in the lane, the steering wheel's green strip lights up, signaling that you can let the car start driving itself. Using advanced GPS, cameras and sensors, the car stays dead center in the lane, deftly handling curves and staying a safe distance behind the vehicle ahead of it.

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A driver-facing camera monitors your eye movement, without recording video, to ensure that you’re still watching the road. At night, it uses infrared technology to monitor your attentiveness.

That’s a feature National Transportation Safety Board members said they want automakers to adopt after a Tesla Model S with Autopilot crashed and killed an Ohio resident who wasn’t paying attention to the road in May 2016. Instead of a camera, Tesla requires the driver to grip the steering wheel so that the vehicle knows the driver is still monitoring the road.

You don't have to touch the CT6 wheel at all while Super Cruise is activated. But Cadillac’s camera doesn’t allow for much distraction.

Anytime I looked away from the road for more than a few seconds, the green strip started blinking, warning me to pay attention.

If the car sensed that I was still distracted after a few seconds, the strip turned red, a chime sounded and the car began coasting, essentially forcing me to take the wheel. If I hadn’t done anything, the car would have come to a gradual, controlled stop in its lane. That's designed to protect a passenger who is suddenly incapacitated.

Tesla's system does one thing on the freeway that Cadillac's does not: It can change lanes when the driver activates the turn signal.

As I sped along on the Capital Beltway encircling Washington, Super Cruise forced me to pay attention to the road several times. In fact, I’d say it sided toward being overly cautious. When I squinted in bright sunlight, the system gave me the standard warnings anyway.

To avoid the warnings, I opened my eyes a little bit more, and the green strip on the wheel turned solid again.

That’s a small quibble. I can deal with it. Better safe than sorry.

Before taking the test drive, Cadillac officials told me that the car could handle stop-and-go traffic on the freeway, just like Tesla's system. It's operational up to 85 mph.

So when I saw construction traffic up ahead — with the car in front of me at a complete stop as I barreled toward it — I figured, well, we’re about to find out.

As the CT6 drove itself, the car came to a slow, natural stop at a comfortable distance behind the sedan in front of me.

Phew.

"It’s the first hands-free driving technology for the freeway," said Eric Angeloro, marketing manager for the CT6. "It’s a nice, relaxing way to travel."

Another time, I was allowing the CT6 to drive itself in the right lane and a pickup was merging toward me from the on-ramp. As the pickup cut in front of me in a moderately aggressive maneuver, my Cadillac slowed down quickly but safely and stayed in its lane.

The other driver waved his hand outside his window to thank me for letting him in. I accepted his gesture of thanks.

But it was really the car that deserved the credit.

Follow USA TODAY reporter Nathan Bomey on Twitter @NathanBomey.