Looking at Google, the rail line is close to the wreck site but not actually under it. Appears to be parallel to the freeway at that point, going into a tunnel north of the 14. There were and probably still are people running all over the place there but it seems unlikely that there was actual damage to the rails. Bigger problem is whether when the fire finally gets knocked down enough to get in and inspect it (news and CHP web reports suggest it's still not all the way out) the freeway itself will need reconstruction. Could be Northridge earthquake all over again, with it being practically impossible to drive between SFValley and Santa Clarita/Palmdale, so Metrolink may have to pick up some slack come Monday.