A government-commissioned report has given the clearest indication yet that the proposed £32 billion HS2 high-speed rail project will be given the go ahead.
Suggested alternatives to the scheme would fail to deal with long-term overcrowding on trains, the report said.
The two alternative schemes, favoured by some of those opposed to the London-Birmingham HS2 plan, would also consign passengers to long periods of disruption.
Prepared for ministers by Network Rail (NR), the report suggests that Transport Secretary Justine Greening will give the green light to HS2 which passes through Tory heartlands in picturesque spots.
A decision on the project, which has sparked fierce and acrimonious debate with Conservative MPs among the anti brigade, is expected in the next few days, possibly as early as Tuesday.
HS2 envisages a high-speed line built initially between London and Birmingham, to be completed around 2026, with a second phase extending the line to north-east and north-west England by around 2032/33.
The NR report looked at two schemes which suggest a series of improvements to the existing West Coast Main Line (WCML).
The report said:
:: Neither proposed alternative scheme would provide enough capacity to meet the forecast demand for commuter services on the WCML;
:: Both schemes would result in long periods of heavy disruption for passengers while infrastructure work is undertaken;
:: Both schemes would slow down the WCML's fast lines and cause congestion;
:: Neither scheme would allow any growth in freight traffic and in some cases would leave stations with fewer or no train services;
:: In the longer term, running the proposed number of additional services would have a significant and detrimental effect on the reliability of the network.
The report also found that while cost estimates for the schemes were "realistic", factors such as remodelling work at Euston station in London had not been included and the cost of disruption had been underestimated.
The report concluded that the proposed schemes "deliver considerably fewer benefits than a new line" and that while they "may offer limited and short-term opportunities for improving capacity on some areas of the route, the requirement for a new line to relieve capacity in the longer term remains and therefore would have to be delivered, in addition to these proposals, in any case".
A Department for Transport source said: "NR has carried out a sober and independent analysis of the alternative solutions to upgrading and future proofing our railways and concluded that patchwork upgrades to the existing rail network simply will not resolve the huge capacity challenges we face.
"Our plans for a new high-speed rail network would increase hugely the number of seats for passengers available on Britain's inter-city railways as well as freeing up space on current railways for more trains to operate and all with minimal disruption to the existing railway."
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