General Question

augustlan's avatar

When cruise control 'hits the brakes', do the brake lights come on?

Asked by augustlan (46577 points ) December 24th, 2013

I go up and down a couple of mountains on one of my regular drives. If I’m using cruise control, it feels like it’s ‘stepping on the gas’ when going up, and ‘hitting the brakes’ when going down – in order to maintain a steady speed.

Do my brake lights come on when I’m going down a mountain? Is it noticeable from outside my car, in other words?

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15 Answers

thorninmud's avatar

Cruise control won’t apply your brakes to slow the car. It downshifts instead, so the resistance of the engine slows you down. Since the brakes aren’t involved, no lights.

El_Cadejo's avatar

As @thorninmud CC doesn’t apply the brakes, it just downshifts and gives the engine less gas.

gasman's avatar

I agree that brakes are not applied. Every cruise control I’ve driven, however, simply releases the throttle and allows the vehicle to coast to a slower speed. No downshifting.

If you step on the brake the system will disengage completely (until you press ‘resume’) and the brake lights come on by way of the pedal as usual.

augustlan's avatar

Thanks, guys!

Wealthadvisor's avatar

According to the Federal Motor Vehicle standards, if your car has adaptive cruise control, the brake lights do come on.

thorninmud's avatar

@Wealthadvisor Yeah, but that’s the kind of CC that uses radar or laser to sense the distance to the car in front of you and maintain a safe distance. If @augustlan has that, we’re paying her too much ;)

El_Cadejo's avatar

@gasman my car would normally release gas and coast down to the speed but if the decrease in speed was enough I could hear it downshift.

kritiper's avatar

Cruise control doesn’t operate the brakes: you do. When the cruise control is on and you touch the brakes, the cruise control gets shut off automatically. When the brakes are applied, the brake lights come on.

augustlan's avatar

I would think it’s got to be downshifting, since it’s not using the actual brakes.

In normal (non-cruise control) driving mode, coasting down either of the mountains with my foot off the gas results in a significant increase in speed. I have to ride the brake periodically to stay at a safe speed. I just assumed cruise control was doing the same thing. I’m car knowledge-deficient. :p

Adirondackwannabe's avatar

I’ve never had a cruise control that slowed the car. It would back off on the gas but that was it. On the other hand, don’t use the cruise control in anything other than sunny conditions. I was using it in rain, going up some hills and it was at full throttle. I hit something, oil or grease on the left side, and that thing snapped left so fast I almost didn’t catch it. It was four huge corrections before the sensor shut it off or I hit the brake, I’m not sure what.

kritiper's avatar

@augustlan – You can manually select a lower gear to keep the speed in check as you coast downhill. That is what they are there for on the selector. A car can gain speed on hills when coasting, this is called freewheeling. It happens when a one way clutch becomes disengaged with the increasing speed of the car going downhill. When you manually select the lower gear, even if the transmission is already in that gear, a band or other device will be applied to stop the freewheeling and you won’t have to apply the brakes to control the vehicle’s speed.

KaY_Jelly's avatar

Your speed is increasing when going up hill because it is trying to stay at the speed you set the cruise control at.

So when going uphill, regardless of the cruise control or not, your car will need the extra speed to help it up.

Also going downhill your brake lights do not come on.

Since you have your car set to a specific speed on the cruise control, while going downhill your car catches momentum so it will downshift or not apply so much pressure because it is set to cruise at the certain speed you set it for, the internal computer knows not to go under or over that number it is engaged at.

Cruise control is no different than having your foot on the gas pedal, but the computer in your car just keeps the speed constant so you do not have to, because a lot of people have a problem with that and they think it saves gas. Sometimes the pedals are in funny spots I think and IMHO that can cause your foot to get tired and it is more difficult to keep the speed constant. My car now does not have cruise control although any other car I ever have had has had it, in the other vehicles I was glad I had it, the vehicle I have now I do not miss it at all, I can keep the speed constant with no issue. The pedal in my car now seems like it is positioned perfectly

Also in cruise control vehicles the only time the brake light comes on is when you physically apply your own foot to the brake pedal which disengages the cruise control.

eno's avatar

The light comes on only when the breaks are applied. However, the breaks can be applied automatically by the computer if you have that technological feature. Although the technology sooner applies to other cars, rather than the type of road. Automatic throttle reduction won’t trigger the lights.

My car does both but the lights will only come on when the computer applies the breaks. Each manufacturer has a different name for it, but the technology is generally the same. On my car, it is called Pre-Collision System with all-speed Dynamic Radar Cruise Control. The radar tech detects the speed of the cars in front of me. If my car gets too close to the cars ahead, the throttle is automatically reduced and the brakes are applied. As soon as the road ahead clears, the vehicle returns to its preset speed.

gasman's avatar

The consensus seems to be that “ordinary” cruise control, which regulates speed only, does not and cannot apply brakes. Adaptive cruise control, by contrast, uses radar to sense distance to the car ahead and may apply brakes to avoid collisions, if you’re closing on it too fast. Adaptive cruise control is a relatively new technology (I haven’t driven one yet) while regular cruise control has been quite common for decades.

JLeslie's avatar

I wondered this also, great question. I almost never use cruise control on verry hilly roads because the cruise control doesn’t do what we are taught to do in driving school. We, as drivers, see the oncoming hill and speed up just a little for more momentum before we start up the incline. When we see a valley we let up off the gas slightly before we start down hill. The car’s computer cannot anticipate the hills and valleys, it must wait to feel it. I always feel like the car is working harder with cruise control in hilly areas, although from what I understand gas mileage is supposed tp be better with cruise control on, so that doesn’t make sense with what I said. Maybe most people have trouble maintaining a constant speed?

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