Quote:
Originally Posted by Busy Bee
talking about maybe a 2-3 foot diameter difference and obviously with a cut and cover construction method would make little difference.
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Minor tunnel diameter differences can exponentially increase the volume of spoil removal and the volumes of steel and concrete necessary to line a tunnel. Pi is a big deal. There are online calculators that are fun to play with but show the terrifying reality of a 23-foot versus 21-foot diameter tunnel.
The new Second Ave. stations have mezzanines that run the full length of the platform (I think - I rode a Q train to the new terminus and back just to say I rode the new line but did not get off at the stations). Such mezzanines are pretty unique to NYC and the other big-time systems. PATH doesn't have them.