[Syonyk]

That's actually one complaint I have about the 1st gen Chevy Volt - the hazards switch is a physical button... on the right side of the center console, over by the passenger. It's not a location that is either rapid to find if you don't know where it is, or particularly rapid to hit when you need them - it's a substantial span reach, unsupported, on a smaller button than I think reasonable. Though, admittedly, I miss the ones on the top of the steering column. That was standard enough for a long time that I still look for the toggle there.

I use them at least a few times a year, though far less than I used to when I was on the interstate a lot more. Any time traffic rapidly drops more than about 20mph, I light up my hazards to let following traffic know, "Yes, you see brake lights, no, they're not just people scrubbing a few miles an hour off - get on your brakes now!" Probably a habit I picked up from truckers, a lot of them do this for the very understandable reason that a big rig doesn't stop on a dime, and even if they will, you're likely to unstack your cargo in the process.

Super infrequently used compared to other buttons, but also not something I really have the time go sorting through menus for when I need it. And neither do I trust the car's automatic systems to turn them on for me.

Though, if I could dream, we'd use LED brake lights to encode braking intensity somehow. The car knows if I'm barely touching the pedal to cancel cruise control and light up the brakes, or if I've just mashed them to the ABS actuation point, but the brake lights don't encode any of this useful info. You couldn't rely on it for car behavior (trivial to spoof, and get rid of tailgaters), but it would be an additional useful input for driving - "Woah, hey, that car in front of you just nearly locked up their wheels, radar data agrees, slow down!"

[frosted-flakes]

Actually, I've seen that some cars will rapidly flash the brake lights a few times if the brakes are applied hard. I don't know off the top of my head which cars though.

[ptaipale]

This is common in newer cars in Europe - if you brake so hard that ABS is activated, the brake lights will flash / pulse.

I suppose regulations do not allow it in the U.S. but at least here it can be programmed on/off via service terminals.

Random example from YouTube: https://www.youtube.com/watch?v=dJk-rJpgF1o&t=108s

[grog454]

Is there a good reason for these regulations in the U.S.? I've seen illegally modified brake light flashing under heavy braking and appreciated it. It catches my attention extremely well (which is the point).

Maybe the concern is that in heavy traffic a sea of flashing lights will overwhelm / distract people too much? Or cause seizures? I'm really not sure.

[hunter2_]

Brake light modulators are many decades old, generally illegal, and therefore aftermarket modifications. The ones that light up like a Christmas tree for feathering the brakes are obnoxious (other than for motorcycles, perhaps), but I'm totally on board with this being standard for ABS situations and similar.

[numpad0]

I heard more than a decade ago that Mercedes designed that system but could not pass regulations back then. Plenty of cars do it today so that must have changed.

[Syonyk]

I've mostly installed them on motorcycles over the years. The combination of a modulator/flasher (several pulses and then solid) and a bright LED tail light makes a HUGE difference in how cars behind you follow - I converted several motorcycles at different points in time and observed the rather significantly increased following distance on each one as I converted them.

I don't know the legality of them, but nobody ever complained on the motorcycles.

[pieno]

This is pretty common in Europe. This may be different because regulation is usually a lot more flexible here regarding car lights (e.g. adaptive headlights) than in the US (although I understand the US is catching up, and there are obviously some areas where the EU has been more strict in terms of daytime lighting and side visibility, mostly for safety reasons).

Most German cars will flash the brake lights when you push the brakes hard, and they will also automatically turn on hazard lights if you brake hard to a (near) full stop (assuming you were going some minimum speed of 50 or 70 km/h).

ABS stepping in is not a requirement as far as I could tell (had this a few times when erring on the side of caution when the light turned yellow). Not requiring ABS makes sense because even if you’re driving on proper roads and your recent German car has great tires and brakes and doesn’t need ABS to decelerate quickly, the truck behind you probably still needs a bit more time and early warning to avoid a collision.

[NathanielK]

Many dealerships install them on all the new cars on the lot, along with protective films and the like. This lets them have a reason for the list price to be well above MSRP without it being a straight dealer surcharge.

[tguvot]

volvo's flash lights in case car things somebody going to rear end it

[ajford]

I think Chevy got feedback on that or something, as that's something they changed on the Gen 2 Volt. The hazard switch is now right by the driver's seat, "down-left" from the shifter.