A REPORT on Britain's first high speed railway raises serious questions about High Speed 2 and shows crucial flaws, technology and engineering experts say.
The Institution of Engineering and Technology warned lessons have not yet been learned from High Speed 1, following research by the National Audit Office.
Passenger numbers for Britain's first high speed railway line which connects London and the Channel Tunnel are still below expectations according to the report.
Campaigners against HS2 have strongly argued that predictions for the number of people who will use the new £33bn rail scheme are dubious.
Chris Richards, Transport Policy Advisor at the IET, said: “In our response to the Department for Transport consultation we made it clear that there were potential flaws in the analysis, several assumptions were made in crucial areas and serious questions have been left unanswered.
“The report backs up our concerns as the original High Speed 1 business case was based on journey time saving benefits and increased rail capacity.
“The total value of these benefits is not known as the DfT has not yet developed a method to evaluate HS1 project costs against benefits, despite this forming part of the High Speed 2 justification.
“High Speed 2 is a project of major national significance, if we get this wrong, we will regret it for decades to come.”
Other key points the IET highlighted from the report are that project costs for HS1 exceed the value of journey time saving benefits, while construction costs were 18 per cent higher than planned.
Passenger numbers were two-thirds of their forecast level, the study found.
The Department for Transport has not yet commented.