a train control system comprising a vital brake interface unit that is disposed between the train control processors and the braking system . the brake interface unit ensures that any failure in the control processors or the interface itself is detectable and , when detected , causes the system to fail safely . by virtue of the use of redundant circuitry paths , the vital braking interface unit enables real - time verification of system circuitry without actually applying the train &# 39 ; s brakes .