The cost of Network Rail's Sheffield to Rotherham tram-train scheme has quadrupled from £18.7 million to £75.1m, according to the National Audit Office (NAO).

In it's report, the NAO stated the project's cost has jumped by 401% and is now expected to be finished by May 2018, two-and-a-half years after it's original December 2015 date.

The scheme, which is being delivered by Carillion, is intended to provide the first transport service in the UK to use both the street tramway and national rail network. The programme involves the existing national rail infrastructure, modifying the tram network and depot, and purchasing vehicles capable of operating on both networks.

In it's investigation, the NAO states a number of factors caused the large rise in costs, including the Treasury approving the project despite the project's wider financial benefits being uncertain, complex electrification design and safety case work, under-developed designs and additional costs in dealing with the condition of assets and the technical innovations required more time than originally expected.

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The NAO said: "As at June 2017, Network Rail had achieved a number of significant construction milestones, including installing new track, the power supply and a tram-train platform at Rotherham Parkgate. It also changed the way it is managing the project.

"The Department and Network Rail have learned lessons from the pilot but it is too early to determine whether the project will realise the wider strategic benefits. The Department and Network Rail have begun to capture the operational issues involved in using tram-trains in the UK and have, for example, established new technical standards for the signalling. Network Rail has shared lessons learned with other tram-train promoters.

"The Department has not yet evaluated the value for money of the pilot project or the extent to which it will reduce the costs of introducing similar schemes in other cities."

To view the NAO's report, visit here

(LM/MH)