Most of these answers can be found at...
http://www.massdot.state.ma.us/Highway/bigdig/facts_figures.aspx
How deep under the city streets did they have to dig?
What is the highest number of lanes?
How many cubic yards of dirt were excavated?
How many stadiums will 16 million cubic yards fill?
How many major freeway interchanges are there?
How many cubic yards of steel?
The number of offramps decreased from 27 to what number...?
How many linear feet of steel-reinforced concrete slurry walls?
How long did the construction take from the moment the first dirt was lifted?
How much did the entire project cost?