Originally Posted by SamS
The person would basically have to be standing on the brakes for the additional indicator to come on, i.e. ABS activated.
If you do ever see an F30 with the extra brake lighting action, look out, because they're either about to avoid an accident, or about to have one.
Don't the hazards also flash when the dynamic brake lights are activated (i.e. you'd know if you had activated them?)