Japan’s most spectacular building projects, including possibly the world’s most expensive road, resulted from deception and falsified data, the former president of the state highways agency has told The Times.

Kuniichiro Takahashi’s admission comes as the hugely indebted Government has rediscovered its addiction to public works and has earmarked nearly 70 trillion yen (£311 billion) in its budget for road and rail building projects over the next decade.

Ridiculing these new “roads to nowhere”, Mr Takahashi said they were almost certainly unnecessary in a country whose population is ageing, shrinking and buying fewer cars every year. However, major road and rail construction continues to be the favourite tool of pork-barrel politics in Japan.

On Saturday a short strip of motorway opened in central Tokyo, joining two parts of the city already saturated with road and underground rail infrastructure. The section of road forms a fraction of three gigantic ring-roads that will circle the capital by 2012 and which, a Tokyo court recently acknowledged, were approved on a faulty premise.

One big rail project - a bullet train linking the cities of Fukuoka and Nagasaki - is expected to cost about £1.5 billion, or £100 million for every minute cut from the journey time between the two cities.

Mr Takahashi’s statement falls on the tenth anniversary of the opening of the Tokyo Bay Aqualine – a 15-kilometre tunnels and bridges project that cost Y113.4 million a metre to build and attracts about a third of the traffic for which it was designed. Mr Takahashi’s traffic projections justified construction of the Aqualine, but he now admits that he “licked his pencil” before submitting them to his political masters – bureaucratic slang for creating false figures. The project was also heavily backed by 33 important construction and steel firms that continue to wield huge political muscle.

Mr Takahashi said: “The idea was to build toll roads, and the Prime Minister or other top politicians would order them built even if they knew they were not profitable. As bureaucrats, we had no choice, even though we studied the situation at length. When we wrote a proposal, we had to cook up figures even when we knew the project would be unprofitable . . . we just licked our pencils and predicted traffic volumes we knew were false.”

He listed other projects, including three toll bridges linking the island of Shikoku to the mainland, which do not stand up to serious consideration, given the falling population.

Mega-projects under way include Tomei 2, a motorway between Tokyo and Nagoya that will take 38 years to build and will, for much of its length, run alongside an existing motorway.

Mr Takahashi indicated that road-building is more about providing jobs and prosperity for economically failing regions outside the big cities than a need for highways.

The ruling Liberal Democratic Party is fighting for survival and can ill afford to give up the trump card of lucrative building projects.

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