The budget for the long-awaited Tram-Train project running from Sheffield to Rotherham has quadrupled from its original forecast.
A report published by the National Audit Office shows the cost of the project has risen from £18.7m in May 2012 to £75.1m in June 2017.
The figure has been labelled a 'disaster' by one Sheffield MP.
The pilot project, funded by Network Rail and the Department for Transport, is expected to be formally completed in May 2018 - two and half years late.
The report also reveals that Government ministers considered to scrap the scheme altogether on two separate occasions due to ballooning costs and lengthy delays.
New calculations on the schemes benefit cost-ratio has slumped from 1.0 to 0.31. Any rating under 1.0 is deemed not to be cost-effective.
A complaint into the delay, lodged by Sheffield South East MP Clive Betts, prompted an investigation by the National Audit Office.
Reacting to the report, Mr Betts said: "It's been a disaster. I find it staggering the costs have gone up so much. The £18m was a low estimation and I think if Network Rail had realised sooner the challenges of what they were actually taking on then we wouldn't be at this point.
"There has been so much time wasted. We mooted this back in 2007 but with it has come many lessons that need to be learnt.
"The report shouldn't undermine the scheme and the potential for tram trains is huge. We could extend lines to Stocksbridge and another through Darnall, Handsworth and onto Beighton which is cheaper and more convenient for the city."
The Sheffield to Rotherham tram-train scheme is intended to provide the first transport service in the UK to use both the street tramway and national rail network.
The Department for Transport identified that tram-train schemes offered the potential to reduce the cost of transport services and create growth by improving access to city centres, but that such schemes could pose 'complex technical and delivery challenges'.
Over the past year, all of the track and junctions connecting the tramway and railway have been installed and the erection of overhead masts between Tinsley and Parkgate are now complete.
Work has also started on the construction of the new tram-train platform at Parkgate, and work continues to raise College Road bridge to allow the overhead power lines to pass underneath.
Commenting on the report, Liberal Democrat leader Tim Farron said: “This project has been a total disaster from start to finish. The fact they can’t keep control on a flagship scheme like this shows what a total sham the Northern Powerhouse really is. This report is an auditors version of a character assassination. It is utterly damning.
“With costs running at 401% over budget it doesn’t give a lot of hope for future projects that were looking to take inspiration from this pilot. My worry is that if we cannot deliver schemes like this on budget what hope do we have for HS2?
“The north deserves better than this. The government are showing themselves up to be frankly useless at delivering anything on time and on budget.”
Rob McIntosh, Network Rail’s London North Eastern and East Midlands Route Managing Director, said: “Sheffield to Rotherham tram-train is an ambitious pilot, a UK first, that will bring new travel choices to people of South Yorkshire when services begin in 2018. The project continues to be complex and challenging but will deliver real benefits for thousands of daily commuters.
“Costs and timescales have moved as the project itself has grown in scope and complexity and has had to incorporate more significant infrastructure changes than originally planned. Good progress is being made and a new project team is now in place and driving the scheme to its conclusion."