This also ran past the same signal and collided with the Dundee train. It is believed that the Castlecary distant signal had stuck in the 'off' ('clear') position and so the drivers of both trains took it that the line was clear. The driver of the Edinburgh train only realised that it was not when he crossed the viaduct and saw that the home signal was at 'danger'. Even a modern-day car would not have stopped in the remaining to the tail lamp (which was flattened). A second accident occurred in Castlecary on 9 September 1968, also a rear-end collision. Following the failure of a signal at Greenhill Junction, trains were required (by Rule 55) to stop at the failed signal and report their presence to Signalman D. Craig at Greenhill Junction via the signal telephone. He would allow them to proceed slowly past the signal, at around , and then report on passing the signal to continue to obey previous signals. This method had worked since the signal's failure the night before and throughout the early morning, but at 09:00, Craig became confused by the presence of four different trains in the Greenhill area. Of these trains, the Down 07:40 Dundee-Glasgow service passed through Greenhill uneventfully, but its passage resulted in Craig being forced to hold the Down 08:30 Edinburgh-Glasgow service north of Greenhill Junction. At the same time, the Up 08:46 Glasgow-Edinburgh service driven by Driver W. Watson, consisting of two six-car Class 126 DMUs, stopped at the failed signal, and when Watson contacted Craig on the telephone, Craig misunderstood the call, believing Watson to be the Down train, and told him that he was waiting for a train at Greenhill Junction. The mistake was furthered by Watson's failure to identify his train. Shortly after, Class 24 engine D5122, crewed by Driver W. McIntosh and Secondman R. Birrell, running light from Glasgow to Perth, arrived at the signal in rear of the Up train. Birrell contacted Craig at Greenhill. Like Watson, Birrell failed to identify his train; in combination with Birrell’s impatient tone, this led Craig to repeat the mistake - again believing that he was speaking to the Up DMU at the failed signal. (Its Rule 55 call had been overdue for some minutes.) He gave Birrell authority to pass the signal ahead at danger, at caution speed. D5122 then set off, but McIntosh took his engine to around .