The bypass, which cuts through three Sites of Special Scientific Interest, 12 archaeological sites, a Civil War battlefield and an Area of Outstanding Natural Beauty, will save 15 minutes at peak times for the average user, says the report. But these savings will only be noticeable for about two hours a day.
"During the remaining hours, and therefore for the majority of the traffic, the time savings to individual vehicles will be relatively small," the document states.
The report was obtained by Friends of the Earth following threats of legal action unless the Highways Agency released crucial information on the economics of the bypass. The agency responded by releasing the report, into the assumed benefits of the road, but has now accused Friends of the Earth of "selectively using the figures" contained within.
"It needs to be seen in context," said a spokeswoman. "They've chosen off-peak travel times when there's less of a traffic problem and they've reflected the worst-case scenarios. The problems exist at peak times."
The Highways Agency says that vehicles using the bypass could take an hour off some journeys and up to 28 lives may be saved over a 30-year period. But Friends of the Earth dispute these statements.
"We've seen no figures to substantiate the claims," said their spokesman Simon Festing. "They've twisted and turned in order to not release any of this information. They have even classed this as an internal report to try and evade the law on the disclosure of documents.
"The Government is spending pounds 100m of taxpayers' money destroying wildlife sites, which are thousands of years old, for an insignificant gain."
Meanwhile, both sides are claiming a victory as the conflict over the bypass project enters its sixth week.
With only another six weeks to go before felling stops under European law, less than 40 per cent of trees have been taken down and the most difficult aspect of the work, the eviction of hundreds of protesters from treehouses, has yet to begin.
Protesters expect more than 1,000 security guards, bailiffs and police to begin evicting the tree dwellers within the next 24 hours. All police leave in Berkshire and Hampshire has been cancelled.
Bailiffs and specialist climbers, who will be used in the eviction process, were expected to be sworn-in this morning and given further training. The evictions will be the most complex, expensive and risky part of the bypass clearance work and could last several weeks. There are now more than 30 camps along the nine-mile route, but the Highways Agency has the legal authority to evict protesters from only six.
The campaigners are still fighting the agency through the courts for possession of the rest.
In anticipation of the first phase of evictions, the protesters have been summoning support from hundreds of sympathisers across Britain. They have also issued appeals to the climbing community to help them defend the trees.
The British Mountaineering Council described the campaigners as "courageous defenders of the environment" at the first British Mountain Festival held at Llandudno, in north Wales, over the weekend.Reuse content