Yes, it's happened before--the July accident on the high speed rail near Wenzhou. Signaling fault--and apparently the same company involved in signal equipment on the HSR segment involved in the accident, is the same one involved in faulty signal equipment on Shanghai Line 10 subway. Both times--deliberate shut-off of the automatic protections and reliance on manual operation. Both times, two trains end up trying to occupy the same space at the same time. Fortunately, in the subway incident, speed at the time of impact was minimal, or else there would have undoubtedly been some fatalities.