Regenerative braking is governed by the law that requires any deceleration of 1.3 metres per second squared, or greater, to activate the brake lights. This regulation applies to all types of regenerative braking, including those that occur when the driver lifts off the accelerator pedal or presses the brake pedal.
Manufacturers can also allow their cars to generate a braking signal for gentler regenerative braking forces than this, but it is not mandatory. DOT guidance inc (Regulation ECE R13H)
