At the transportation museum in London, there was an exhibit showing a strip-chart recorder which would measure horizontal and vertical accelleration as the underground trains went through tunnels; the readouts from those recorders could then be used to identify sections of track that needed maintenance.
I wonder if an electronic system might be useable today to perform such a function. Running a tester-train over the track while taking detailed measurements might be a useful adjunct to visual inspection, and if such readings were also taken on normal trains and kept for a week or so it would allow track problems to be researched both on an ongoing basis and after any accident.
From what I've read (real quickly, in the 10 minutes or so) the railroad engineers are performing visual inspections as they go, however, the FRA (Federal Railroad Administration) has a specially designed train for inspecting track geometry.