It's not. No system involving electronics is EVER "fail safe". About 4 months ago, they put up signs under the yellow RR crossing warning signs: "NO TRAIN HORN". They're trying to cover their posteriors for when the gate fails, but I don't think drivers are going to understand that that means "LISTEN" doesn't apply here.
It fails on a conservative estimate about once a month. The window between the failure of the gates and when the trainmaster notifies the engineers is the window where a fatal accident is going to happen, sooner or later.
Duplication of systems (gates, crossing bells and lights, train horn, train bell) is the best way to cover that window.
The train was here LONG before this suburb existed. I had no problem with proximity to the southbound horn from 1994 to last year. I used to investigate crossing accidents, and when you've taken photographs of some poor moke's remains crushed inside his car a few times, it gives you a different perspective.
If a system is "fail safe", that means that a failure will not create a hazardous condition. For example, if the system included a couple accelerometers for each gate along with a couple of current sensor for the lights, and those devices were to all report their status to a couple of differently-designed processors, each controlling a relay that feeds the "no horn needed" light, there are many ways the system could fail such that the light wouldn't illuminate, but if that occurs the only effect will be that the engineer sounds the horn. For the system to fail so as to create a hazard, either the lights would somehow have to draw the right amount of current while not illuminating and the accelerometers would have to report the gates were at the proper angle even though they weren't, or else both receiving processors would have to fail simultaneously at the same time as the crossing gates failed. Highly unlikely.