The EU has approved G-triggered brake lights that do just that, flash rapidly on hard braking. I’ve only seen it on higher end cars so far, but they absolutely exist. Unfortunately in the US people stick brake flashers that blink in patterns every time they touch the brake. Mostly useless as they’re installed to be “look at me, aren’t I cool with my blinky brake lights?” rather than any additional safety.

Reading through the article, it seems like one scenario is that a vehicle stopped at an intersection might be about to pull out, endangering another vehicle about to cross? It seems like the thinking is, if you notice a front/side brake light stops being lit as you approach the intersection, it might indicate they're about to accelerate - be cautious!

I'm not fully convinced either, it seems like a lot of the benefit they're projecting is based on analysis of historical collisions, rather than any kind of experimental results. It sounds like the study is to justify expanding research to that sort of simulated experimentation, though - I'm curious what that kind of testing would find.

They also indicate slow moving road hazards like a semi carrying an oversized load

Faster blink is already used to indicate that one of the lights is burned out. It's a consequence of the mechanical part that operates (used to operate) the blinking; less resistance caused by a burned out light means it blinks faster

I'm pretty sure most cars have a turn signal near the headlights, and one on the mirror or on the side for that use case, no?

Actually I think I remember watching a technology connections video about how card in the US can use the headlights as a turn signal, or something like that.
I don't think that's allowed in Europe or the EU or whatever.

Found it
https://www.youtube.com/watch?v=O1lZ9n2bxWA

hybrid/electric cars already do it with regen braking.

Not all of them. It is becoming more common, but for a while Hyundai and Kia didn't do this, and I know my older Ford doesn't.

Probably just in the US, since brake lights are only required when pressing the brake pedal. Mercedes illuminates them but then turns the brake lights off once the vehicle comes to a stop using regen.

There was an EU rule about ten years ago that stipulated that rear lights are no longer mandatory in daylight. The reasoning being to save on fuel. Which is a ridiculous reason, even more so with today's LED lights.

I don't know about other EU countries but this was the reason that Sweden removed the requirement.
All cars in Sweden used to have the rear lights turned on at all time, even if the light switch was in the off position, but that changed around the same time.

Reminded me of this Technology Connections video, in which the dude explained (among other brake-light related things) how some law allows electric vehicles to get away with not using their brake lights:
https://www.youtube.com/watch?v=U0YW7x9U5TQ

I've seen newer cars turn the headlight off while the turn indicator is on, so you get a sort of double-blink effect

Those are typically DRLs. Chrysler did this for a while in the 2000s-2010s (maybe still, idk), where the high beam - in DRL mode - turns off while the turn signal is doing it's thing. Other manufacturers do this with dedicated DRLs, sometimes integrating the DRLs and turn signals into one multicolored unit (Kia Telluride, for example).

No manufacturer shuts off a headlight for a turn signal when the headlights are intentionally turned on (whether by light sensors at night, or by the driver).

There are a couple situations where it's annoying and I turn it off. My truck has the "steer back into lane" style assist, but it's tried to push me off the road before while I was towing a trailer on some narrow 1-lane roads. Some of the corners it's just not possible to get around without touching the center line.

The vast majority of the time it stays on though and is quite helpful.

that stipulated that rear lights are no longer mandatory in daylight.

I don't believe these were ever mandatory in the EU? UK never had such requirement.

Edit:

What I mean is there are EU countries where lights are still mandatory and countries where it isn't so I cannot see how it could be linked to EU requirements either way.

I see a lot of those on trucks here in the south. Good for when you are towing shit so people can see around all your junk in the trailer.

Colorblind person here. If we're talking about limited visibility differentiation of front and back, the color of light is way less noticeable than whether we're looking at headlights or not (based on intensity). There would be no issue telling whether we're looking at a front brake light or a back brake light so long as the front brake light has headlights around it.

Yeah my electric 208 is kinda like that (if I remember the video well, watched it a while ago) but since it's Europe there actually is a regulation about how much a car can decelerate before break lights come on, so instead of making the system turn the lights on they throttle how much it can decelerate for recharge and still makes you use the break to use full regen (and eventually the actual brakes, of course). So it's not a real "one pedal driving".

I think some cars also turn on the hazards automatically if you really hammer the breaks.

Okay Verstappen calm down there

Since we're all throwing random ideas out here, I want to equip my vehicle with an annoyingly loud external speaker so that when someone near me does something dumb, I can personally shame them.

There's this idea I've been considering for a long time.

Imagine putting a remote controlled firework smoke bomb under the tailpipe, hidden from sight. At best a really stinky one that smells like burned rubber or something.

When someone follows to closely, just fake an engine issue or something by activating the smoke bomb and fill their AC air intake with the smell of burned rubber for weeks. Just to teach them to not follow too closely again.