On two separate occasions, brakes failed completely in snow. Vehicle did not appear to be hydroplaning, and anti-lock function did not kick-in despite the pedal being floored. Pumping had no effect either. Safety sensors around the car should have detected motion even if the wheels were locked-up and should initiate anti-lock procedures as well. Distance traveled (at low speed due to snow and heavy traffic) was well over 100 feet. Emergency stopping feature finally engaged anti-lock brakes about 1/2 second before impact. To avoid a second crash (someone two vehicles ahead caused a pileup) a year later, driver had the wherewithal (and space) to leave the roadway when brakes failed to even slow the vehicle.