But safety investigators may require more than a year-and-a-half to determine the exact causes of the February 20 crash at Wallan, north of Melbourne, with 153 passengers on board.

The train far exceeding the speed limit for a passing loop near Wallan was confirmed in a preliminary report on the crash released by the Australian Transport Safety Bureau on Friday.

"The train was not able to negotiate the turnout to the loop track at this speed and derailed. All vehicles derailed excepting the rear power car," the report reads.

The derailment of the XPT train from Sydney to Melbourne killed experienced driver John Kennedy, 54, and 49-year-old train pilot Sam Meintanis.

The pilot had joined Mr Kennedy at the front of the train only a few stops before Wallan to help him navigate a 24km-section of track where signalling equipment was damaged, as part of an "alternative safeworking system".

The equipment had been damaged by a fire in a track-side equipment hut on February 3.

After setting off from Kilmore East bound for Wallan, the train increased toward its speed limit for the section of 130km/h.

Earlier that afternoon, the points - or movable rails - at either end of the Wallan Loop had been changed so that rail traffic was diverted from the main line into a loop track.

There was a train notice flagging the change and specifying a speed limit of 15km/h for entering the loop and 35km/h for exiting.

Data from the train show an emergency brake was applied shortly before the train reached the points.

"This slowed the train a small amount before it entered the turnout travelling at a speed in excess of 100 km/h," the report states.

The derailment that followed left the driver and pilot with fatal injuries, while three passengers was also seriously hurt.

Another 36 passengers received minor injuries, along with five train crew.

ATSB chief commissioner Greg Hood stressed the preliminary report is aimed at establishing basic factual information.

A final report which could take more than 18 months to prepare will detail findings, including contributing factors and any safety issues.

"However, should any safety critical information be discovered at any time during the investigation, we will immediately notify operators and regulators, and make that publicly known," Mr Hood said.

Further investigations will include a detailed examination of the operations of the train.

The alternative safeworking systems used to manage rail traffic at the location in the two weeks leading up to the crash will be put under the microscope.

The condition of the track and vehicles will be further investigated, through data collected so far has not identified anything in either that can be linked to the derailment.

Australian Associated Press