[oh_sigh]

I can go from 75 to 5 mph in my ICE with the brake lights never coming on. Or, I can maintain 75 mph with my brake lights on 100% of the time.

But really, there should just be a standard - it seems obvious and easy for EVs to get it right: If deceleration is > X m/s^2, then brake lights are on.

[WelcomeShorty]

The European Union has a regulation that requires EVs to illuminate their brake lights anytime the regenerative-braking system’s deceleration rate exceeds 1.3 meters per second squared, or about 0.13 g.

[throwaway2037]

Cool. How did you know this incredibly specific value? Assuming that it is correct, how was it determined? I would like to learn more.

[WelcomeShorty]

Simply because I've been driving TVs for a while and "in the beginning" when there was no rules for brake lights to be turned on when regenerative breaking, I got into trouble (German highways) with cars driving behind me and not being able to anticipate / react fast enough when I used it.

I quickly learned to force the break lights and started to follow this issue closely. That's how I became aware of the number.

How the EU saddled for 1.3 and not 1.2 or 1.4 is beyond my knowledge.

[gnicholas]

Unless I downshift using paddles, my ICE will coast forever from 75. My PHEV, on the other hand, will slow down much faster. I want my PHEV to illuminate the brake lights if I'm decelerating above a certain rate, just as you suggest.

It never occurred to me that I might want my ICE to do the same, but I suppose it would be helpful if I'm heading downhill and downshift without touching the brake.

[perilunar]

How will we then be able to tell which drivers are ignorantly riding their brakes all the way down a long hill, versus the drivers using engine braking?

[tristor]

By listening? Engine braking makes noise, which is why it’s banned in some areas.