A report released by the Australian Transport Safety Bureau yesterday said the train came off the rails at a section where the track splits in two.

It was the first time the XPT had used that type of intersection, which is known as a type 37 mixed gauge turnout.

Two carriages on the 8.30am service derailed on July 11 as the train was headed north just 3km out of Melbourne.

It took two hours to evacuate about 180 passengers who were left waiting to catch buses to their destinations.

Commuters from the Border and North East were forced to use replacement bus services for more than two weeks between Broadmeadows and Southern Cross Stations while the track was being fixed.

The investigation found the train left the track as it transitioned from standard gauge to broad gauge at the type 37 intersection.

Earlier that day, the same train derailed at another type 37 turnout on its way into Melbourne but re-railed a short distance later.

The first incident was reported and was undergoing investigation when the second derailment occurred.

According to the transport safety bureau, rolling stock was found to have played no part in the derailment.

The fault was with the approved design of the type 37 turnout, which hadn’t been properly tested to support the narrow wheel rim width of rolling stock like the XPT.

“It had been assumed the type 37 turnouts would perform safely in service based solely on the performance of a similar (type 29) dual gauge turnout, although there were significant differences between the two turnout types,” the report said.

V/Line has since managed the redesign of the type 37 turnouts so standard gauge rolling stock can now operate safely on them. It also reviewed contractual arrangements and testing and commissioning.