[PNWmisty]

I wish it was optional for regen to trigger the brake lights. Between Autopilot freaking out, aggressive braking behavior when speed limit changes while using TACC, and just trying to coast in general, other drivers must think I don't know how to drive.

Federal regulations specify a rate of deceleration that must trigger the brake lights so it's not an option for Tesla to make it optional. And if you're just trying to coast but accidentally go into slight regen, that's not enough to trigger the brake lights so I don't think you need to worry about what other drivers think.

 

[PNWmisty]

The LEAF doesn't trigger the brake lights, even at max regen (although it's only 30kW). Any idea what regulation this is, and if this would apply to manual transmission vehicles (mostly curious)?

Manual and automatic transmission ICE vehicles are only required to illuminate brake lights when the brakes are activated. Since electric cars have regenerative braking, they have their own regulations.

https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R13hr2e.pdf

Look under UNECE 13H

5.2.22.4. Electric regenerative braking systems as defined in paragraph 2.17., which produce a retarding force upon release of the accelerator control, shall generate the signal mentioned above according to the following provisions:
Vehicle decelerations

Signal generation
≤ 0.7 m/s² The signal shall not be generated
> 0.7 m/s² and ≤ 1.3 m/s² The signal may be generated
> 1.3 m/s² The signal shall be generated

In all cases the signal shall be de-activated at the latest when the deceleration has fallen below 0.7 m/s².

It does feel embarrassing as it looks like I'm slamming the brakes when AP/TACC drops to follow new speed limit (e.g., 40->35).

I don't understand this. All vehicles brake lights come on when your foot touches the brake pedal, even if only applying the brakes very lightly.