More than 1100 different “conflicts” between underground pipes and cables and tram works have been discovered between Haymarket and York Place, sparking fears of extra costs being piled on to the troubled project.
Tram bosses have been carrying out a series of tests along the 1.3 mile-section of the route between Haymarket and St Andrew Square.
They today confirmed a new estimate of 1100 different “utility conflicts” – clashes between water, gas, electricity and other cables or pipes and the proposed design of the tram line, including locations for overhead cables.
The figure comes after further investigations in recent months and is double the number of conflicts that councillors were told about in a report to council in August.
Designs will need to be redrawn to work around the cables and pipes in most of the cases, while utilities will need to be physically diverted at around 150 different points.
The extent of the extra work required has led to fears that it could result in project costs rising above the new £776 million project budget that the council has agreed.
Councillor Jeremy Balfour, leader of the Conservative group on the council, said: “We always said we did not believe the figures and we were always concerned that there would be real problems with the on-street works and that is why we voted for [finishing the line at] Haymarket.
“There are still lots of risks with this project and we do not know what the final bill will be, so people are rightly concerned and we are concerned.”
The £776m figure resulted in the council having to borrow £231m, but Cllr Balfour believes that more money will still have to be found to complete the project to St Andrew Square.
However, project sources insist that the number of utility diversions required is within what they expected and say that it can be completed within budget.
The £776m project costs includes £34m set aside as “risk and contingency”.
It is understood that the council remains hopeful that the risk fund will prove enough to deal with the cost of utility diversions and other overspends.
One senior council source said: “Currently there are 1100 clashes on-street from Haymarket to York Place but, of these, only circa 150 are likely to require diversions. The rest can be designed around so we don’t have to remove them.
“It is not that we won’t use our risk allowance, but in terms of the first part at Haymarket we are well within our budget.”
However, the figures are estimates mainly based on drilling bore holes in areas known to contain utilities, and may rise once further work is carried out.
It remains unclear why some of the utility conflicts were not picked up earlier in the project.
The source said: “Some of these utility diversions should have been diverted in the past but weren’t.”
Cllr Lesley Hinds, transport spokeswoman for the Labour group, said: “It was always the concern with the St Andrew Square option that there was more risk involved as there was more disruption on the road and more utilities on the route that may be in conflict.
“It gives a concern that, if there are that many utilities in conflict, have they put enough contingency in for the cost?”