But it has emerged that the trains the government initially planned to order would be able to run only on intercity lines because they would be too long and narrow for underground platforms on Sydney's suburban network, which are usually about 170 metres long. In contrast, platforms at regional stations are about 200 metres. The new trains have been ordered to service the Blue Mountains, the Illawarra, Newcastle and the Central Coast. Credit:Adam McLean Existing trains in the state's fleet such as the Tangara G-sets and Oscars are suited for several roles. They can run on inner-city lines to underground stations such as Wynyard, Town Hall and Martin Place, as well as plying outer suburban lines to Wollongong, Springwood in the Blue Mountains and Newcastle. At present, almost a quarter of the trains that run on the suburban network during peak travel hours are tagged "regional rolling stock", helping transport officials to maximise their use and plug any gaps. "The mistake they made is that they wanted a single-specification train to operate on the regional intercity services and have overlooked that such a train set would be incompatible with the inner suburban underground network," an insider said.

Transport for NSW has blamed "operational and network changes", the inclusion of a new maintenance facility and currency fluctuations for the $1.1 billion surge in the project's cost. Gladys Berejiklian's natural caution has contributed to a remarkably low profile for a NSW Treasurer.. Credit:Max Mason-Hubers However, the department said it was too early to give detailed cost breakdowns that "might be required to introduce the fleet to the network". "While we're aware of the high level requirements, the tender process will give us more detail on operational requirements to suit the particular train solution proposed by the successful consortia," it said. The department declined to reveal any detail about what changes to trains or carriages would be required, citing commercial sensitivities.

Shadow transport minister Ryan Park said it was a "very expensive mistake" if the government had to reconfigure the train fleet to fit the network. "A $1.1 billion blowout because of a failure to take into account major fleet modifications, budget for foreign exchange fluctuations or the cost of a new maintenance facility is breathtaking," he said. "Cost blowouts on major infrastructure projects are becoming alarmingly frequent." A spokesman for Transport Minister Andrew Constance said the train tender had been affected by foreign exchange rates and now had one budget that was rolled together from different projects. "If Labor was running things they'd probably cancel it, reannounce it, spend millions and then cancel it again," he said. Kangy Angy on the Central Coast is the preferred location for the new maintenance facility for the intercity fleet. Transport for NSW would not reveal the number of trains it will be able to handle or its construction cost because it had yet to go to tender.

The department said it still expects the first of the new trains and carriages to be delivered in 2019. It is set to award the multibillion-dollar contract to supply and maintain the new intercity fleet next year to one of four short-listed consortia. They include Australian engineering company Downer EDI and Chinese partner Changchun Railway Vehicles, which were behind NSW's once-troubled Waratah train contract. Downer's rival, UGL, is part of another consortium vying for the NSW government's first order of new trains since 2006.