Investigators say a Tasmanian train that derailed late last year was travelling at almost double the advised speed.

The crash in the state’s south cost operator TasRail $3 million, and the Australian Transport Safety Bureau's (ATSB) preliminary investigations have indicated that the speed was a major factor.

The section of track near the town of Colebrook features several steep sections and tight curves, so it is signposted at 35 km/h.

But the authorities say the train was travelling at closer to 64 km/h when it leapt from the rails last November.

Two locomotives and 11 wagons left the track.

The exact section of track was upgraded with new concrete sleepers in the months before to the accident, but it was well known as a trouble spot.

The ATSB’s initial report found the train could not safely negotiate the curve at the speed it was travelling

“The leading wagons lost their containers to the right, one of which impacted the bridge abutments, before the locomotives and leading wagons overturned, rolling over the right hand rail,” it said.

“The remainder of the train was brought to an abrupt stop; causing further wagons to derail and some containers to be cast to the left of the track.”

The report is accessible here.