Adaptive cruise control question

The adaptive cruise control uses regeneration to slow you down on a downhill, just like pressing lightly on the brake pedal. It won't use engine braking unless the battery is full and thus regeneration has nowhere to put the energy.

I believe that it lights the brake light, but someone else should confirm.

 

Regen illuminates the brake lamps.

 

I've read from several places that it turns on the brake lights but never had someone follow me to confirm.

 

Has anyone done a test? I'm 99% sure the brake lamp is on, when the adaptive cruise has to actively brake for traffic; but what about regen on a "glide", like dropping down into an underpass. I'm behind Primes all the time and don't see the brake lamps light-up. I'm following the same path and I see my car going into regen. I'm pretty sure, when you downshift to B, the brake light aren't on.
See article. https://www.greencarfuture.com/electric/does-regen-braking-turn-on-brake-lights
I know some Tesla's has a one pedal function, and the article wasn't clear if the driver was using that function. You take your foot off the accelerator and the car automatically brakes. If this function was active; of course the brake lamps should illuminate - because you are braking..

BTW; I have a habit of turning-on my hazard lamps when I round a corner and there's slow moving traffic or cars braking in the distance. I developed this habit, when I was rear-ended a couple of times when traffic came to an abrupt slow-down or stop. Last car into the traffic jam usually get hit. Haven't been rear-ended since.

 

I have a Prius without adaptive cruise, and I am pretty sure that most occasions for regen (foot off accelerator, or B mode, or normal non-adaptive cruise holding speed on a downgrade) do not light the brake lights. The brake lights do light when you press the brake pedal.

It would be my starting assumption (maybe to confirm with someone following behind) that the adaptive cruise also isn't going to light the brake lights during ordinary speed-holding operation, but only when it actively slows because of something in front.

 

Yes, the brake light will come on but depending on how hard the car brakes to maintain the set speed. I have confirmed this on my long trip on a highway at night. I could tell when the brake lamp is lit. On very steep downhill or very sudden braking due to a car in front of me slowing down, the car brakes hard and the brake light comes on. But if it is a very gradual slow down then it does not. The behavior is very similar to pushing the brake pedal. It has some amount of play before it triggers the brake lamp.

 

I haven't confirmed the brake lights on during motor braking either. Notice the OP said Motor braking. Engine braking on the Prime is way different compared to motor braking and or regenerative braking, whichever term you want to use.
Before started using standard Cruise Control by holding the cruise control On/Off button in for 5 seconds to activate it, I found a weird quirk using the radar adaptive cruise control. At highway speeds if you hold down the cruise control stick on the steering column for 5 seconds approx. the cruise control will slow the car extremely fast. It's not a freature / quirk one wants to use if anyone is closer than about a half mile behind your car, just in case the brake lights are not on when slowing at that rate.

Slowing at both regenerative braking or even B mode is not anything I ever worry about, since B mode slows the car even less quickly than most manual transmission car when they downshift.
Another option is to feather the brake pedal while the car is motor braking. With a sensitive enough feathering of the brake pedal the brake lights (should get switched on - not confirmed either), and use little to none of the pads on rotor brakes while doing it as part of the brake pedal travel only activates regenerative braking anyway.

 

I use this feature often when moving from one speed limit zone to another and I can confirm the brake lights come on, just as if you are using the brake pedal (I’ve seen glow at night on road signs). If you click to slow done in 1 km/mile increments, the lights do not come on. If you hold the lever down for 5km/mile increments, the lights do come on. I find this feature incredibly useful as I have a chronic leg pain and anything I can do to avoid an unnecessary movement from accelerator to brake on a long drive (my one way work commute is 160km/100 miles) is a boon. Of course, when weather conditions don’t make it safe, I grin and bear the pain. But having had it for nearly a year (and 43,000km), I will never buy a vehicle without adaptive cruise control as a daily driver again.

 

@Ovation Thanks very much for explaining that. I was not aware, it never occured to me to check how fast the car was slowing down when holding the cruise control stick down. I'll tell you it seems a lot more speed reduction than 5 mph / ? second? in my 2017 Prime Plus. But I'm holding the stick down continuously from 65 mpg until adaptive cruise shuts off at 32 mph. I also can't think of a better way to describe it to other drivers.
Like how much pressure on the brake pedal it's equivalent to. That probably depends on how sensitive one persons foot on the pedal is comparing to another persons pedal pressure.
I am glad that the feature helps reduce some pain and is handy in more respects than just the occasion use.