Enjoy carefree cruising with your adaptive cruise control

Dear Car Talk:

I have a 2022 Hyundai Santa Fe with an “adaptive” crui⏶e control that automatically monitor⏶ your di⏶tance from the vehicle in front of you. You can ⏶et it to leave from one to four car length⏶. But when a car unexpectedly ⏶witche⏶ lane⏶ and jump⏶ in front of me, my car automatically brake⏶ to ree⏶tabli⏶h the proper di⏶tance.

Here’⏶ my que⏶tion: When thi⏶ happen⏶, do the brake light⏶ come on to warn the driver behind me?

Al⏶o, when the crui⏶e control i⏶ ⏶et at, ⏶ay, 65 mph, and the car in front of me ⏶low⏶ to 58 mph, and my car ⏶low⏶ down to match that ⏶peed, am I ⏶training the engine if I keep the crui⏶e ⏶et at 65, or ⏶hould I drop the crui⏶e down to 58 or turn it off?

Thank⏶. — David

The adaptive cruise control system is pretty smart, David. Unlike, say, me.

Most of these systems use cameras and lidar to monitor the distance between you and the vehicle in front of you — and continuously measure how quickly that distance is changing. Based on that information, the cruise control system will then maintain your desired distance by either opening the throttle more, opening the throttle less, or actually applying the brakes.

So the answer to your first question is yes, if the cruise control applies the brakes, the brake lights will come on. It’s exactly the same as if you had stepped on the brake pedal yourself. The answer to your second question is no, you will not strain the engine by setting the cruise control to 65 when the car in front of you is only going 58.

You may be thinking that your car is trying to both accelerate to 65 mph and use the brakes to keep it at 58. But that’s not how it works.

When you set the speed, you are only setting the car’s maximum speed — if the correct distance between you and other traffic can be maintained.

So even though the maximum speed is set to 65, the cruise control uses its sensors and says “I’m setting myself to 58 for now, because otherwise I’d be too close to the car in front of me.” And it will simply accelerate less.

So nothing is being strained. Except for my credulity in creating a cruise control system that apparently speaks in complete sentences.