Car Talk: Enjoy carefree driving with adaptive cruise control

Also, when the cruise control is set at, say, 65 mph, and the car in front of me slows to 58 mph, and my car slows down to match that speed, am I straining the engine if I keep the cruise set at 65, or should I drop the cruise down to 58 or turn it off? Thanks. — David

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.

Got a question about cars? Write to Ray in care of King Features, 628 Virginia Drive, Orlando, FL 32803, or email by visiting the Car Talk website at www.cartalk.com.