NECR's Bellows Fall tunnel is cleared to a minimum height of 19' 8" which will not accommodate double stacked domestic cube containers but will accommodate enclosed auto rack cars and double stacked international cube containers or 1 domestic cube container and one international cube container. In other words, its vertical height clearance accommodates the same auto rack and container configs as Pan Am's Hoosac Tunnel.
Here's a link to a detailed illustrated project description for the 2007 enlargement (note how the canal bridge at one end of the tunnel and the grade crossing at the other end necessitated short 4% grades coming out of the tunnel in both directions):
http://nec-sia.org/pdf/Bellows%20Falls% ... roject.pdf
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