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Boston tangler A mass of tunnels and viaducts is being constructed to make a crucial interchange in the middle of Boston, without interfering with the smooth flow of traffic.

What is almost certainly the most expensive and complicated interchange in the history of world highways is beginning to take shape in the centre of Boston. A three dimensional nightmare of tunnels and viaducts, the South Bay interchange, has to be completed within three years, at a cost of $397M (£244M), while keeping 190,000 vehicles a day flowing freely through the centre of the site.