On February 11, 2011, a KTX-Sancheon train bound for Seoul from Busan derailed on a switch in a tunnel before Gwangmyeong Station, when travelling at around . No casualties were reported, only one passenger suffered slight injury, but KTX traffic was blocked for 29 hours while repairs were completed. Preliminary investigation indicated that the accident resulted from a series of human errors. Because workers improperly repaired a point along the tracks. Investigators found that the derailment was caused by a switch malfunction triggered by a loose nut from track, and suspected that a repairman failed to tighten it during maintenance the previous night. The switch's detectors signalled a problem earlier, however, a second maintenance crew failed to find the loose nut and didn't properly communicate the fact to the control center, which then allowed the train on the track. The rail union criticised Korail's use of hired repairmen. there were no problems with the train according to investigation.