Today's Boston can't even build a traffic tunnel. The Big Dig was a disaster-- took decades, costs billions more than planned, and was so shoddy the finished roof fell and killed someone. http://en.wikipedia.org/wiki/Big_Dig
They should have eliminated the Big Dig completely and spent the money on increasing rapid transit capacity.
That said, eliminating the elevated highway that cut the North End off from the rest of the city seems to have been a major boon.
[1] http://en.wikipedia.org/wiki/Law_of_demand
[2] http://www.boston.com/news/local/articles/2008/11/16/big_dig...
But I did want to add that it isn't only the north end that was cut off. I doubt the resurgence of the Sea port area/"innovation district" would have happened if it hadn't been for the big dig.
Every time I see a cathedral or dom tower ... :)