But the biggest risk identified in the internal review, kept under wraps by the O'Farrell government, is in moving more than 2000 subterranean services, cables and pits throughout the city centre. These items need to be moved so they can be accessed when a tram line is built on top. George Street: Bus routes scheduled to change as early as June. Credit:Andrew Quilty The latest internal estimate of the cost of moving those services is $75 million, up from $44 million when Premier Barry O'Farrell and Transport Minister Gladys Berejiklian said they would build the tram line in mid-2012. But Evans & Peck, contracted to assess the business case for the project, says this is still likely to be an under-estimate. ''It was apparent that the number of services identified within the schedule has significantly increased in quantity across all routes, however the full impact of such utility diversions does not seem to have been adequately captured within the cost plan,'' says Evans & Peck's peer review, conducted in mid-2013.

Evans & Peck says the companies that own the cables and pits - such as Telstra, Optus and Ausgrid - do not have an incentive to meet the government's tight timeframes or do the work on the cheap. "All project risks and contingencies are contained within the $1.6 billion project cost": Gladys Berejiklian. Credit:James Alcock ''It is unlikely that the work will be carried out in a timely co-ordinated way by the utility providers for the benefit of the Light Rail project, thus leaving a high risk of project cost (and time) increases,'' wrote the reviewers. ''Evans & Peck is of the opinion that the rates used do not reflect the cost of achieving these works,'' it said. The review says Transport for NSW has budgeted $11.5 million to move underground Ausgrid cables and pits. But it says this estimate is based on ''very low'' assumptions, and Ausgrid would be highly sensitive to anything going wrong. In March 2009, for example, excavation near an Ausgrid pit resulted in a two-day city-wide power outage. ''Given the risk of a repeat of a city-wide outage during the execution of the diversions work, it is likely that Ausgrid will be extremely vigilant about the possibility of such a strike happening again through onerous requirements around this infrastructure.''

The other big risk identified is in managing the major traffic changes required to build the line. ''We feel that the allowance for traffic management is neither appropriately nor proportionally applied to account for the complexities associated with George Street … and the relative space and ease of construction in some other areas,'' the review says. Under the government's timetable, early works on the line will start this year and construction should be finished by 2018 or 2019. But major works cannot begin in the city until late April next year, because of the 2015 Anzac Day march to commemorate the 100th anniversary of Gallipoli. Ms Berejiklian said: "All project risks and contingencies are contained within the $1.6 billion project cost.'' OFF THE RAILS

- Tram from Circular Quay to Central Station, Randwick and Kingsford - To be built by about 2019 - Estimated $1.6 billion cost Loading - George Street to be closed to traffic during construction

- At least 2000 underground cables and services to be moved