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

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.

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.

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.

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.

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.

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.

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