An electropneumatic rail brake system configured to provide emergency braking including an emergency magnet valve which controls air flow into an emergency regulator valve, which valve has an emergency back-up chamber. The emergency regulator provides an output pressure nominally equal to the variable load pressure and no lower than the tare back-up. The magnet valve is closed when energized and when de-energized, pressure is allowed into the emergency back-up chamber, Regulation of the brake cylinder pressure continues during an emergency application such that the brake cylinder pressure applied during an emergency stop does not drop below a predetermined level. In the event of power-loss during an emergency brake stop, the nominal emergency brake pressure is applied to the brake cylinders.