Answer, too rare a line to know.

How about 2050 foot length tunnel in Farmams, Mass. north of Pittsfield, MA. Built by the Farnams-Cheshire Lime Company westward through a mountain to a quarry on the west side which was 180' deep and 350 feet in diamenter. It used 9 Whitcomb engines by and after April, 1930 when it was bought by U.S.Gypsum, who owned the nearby New England Lime Co. U.S.Gypsum disassembled their NEL Co. Shay #2306 and moved it by dirt road into the quarry where it worked isolated for a number of years with out being able to pass through the tunnel. That was because the tunnel was only 10' in height and 20' wide. The stone loads in the tram cars was crushed by the roof of the tunnel up into the 1950s when a new under mountain exploration for new stone hit a underground river and flooded the entire operation. The mill buildings still stand at Farmam but the 2 miles of 3' railroad were removed except in the tunnel.
The Hoosac tunnel was the next longest tunnel in Mass. PRR