Speed restrictions have been applied on northern lines when the temperature reached – or passed - 33 degrees. V/Line communications manager Rob Curtain said the restrictions were applied during hot weather, to reduce the risk of derailments.
“Completion of works associated with the Murray Basin Rail Project will increase the lateral stability of the track on V/Line’s freight network,” Mr Curtain said.
The works would mean the temperature at which heat speed restrictions were implemented would be 36 degrees. “At that point, the speed of trains will be reduced from a maximum of 80 kilometres per hour (kph) to a maximum of 50kph.”
Engineers Australia transport spokesman Chris Warnock said applying speed restrictions was standard operating procedure, when air temperatures exceeded a nominated level.
“The basis for this practice is typically related to track infrastructure type and its condition,” Mr Warnock said. “In excessive heat conditions track may buckle suddenly, associated with the expansion of the steel rails, resulting in an elevated derailment risk.”
He said modern track clips provided much greater strength than the old ‘dog spikes.’
The weight of the sleepers, with modern prestressed concrete sleepers providing much greater resistance than steel or old timber sleepers, and the type and condition of the ballast, also had an impact on derailments.
Mr Warnock said the nominated temperature, at which the speed restrictions applied, were usually determined by the rail operators, based on their assessment of track and seasonal atmospheric conditions. “Sudden changes in temperature are more likely to cause track buckles than prolonged periods of sustained temperature. Nominated temperatures for speed restrictions in outback Queensland are typically 38 degrees,” he said.