The Hoosac Tunnel was one of the great railroading and engineering projects of the 19th century, blasting a huge hole through a mountain in order to help trains to traverse the immensely hilly terrain of of New England. It is on the Boston & Maine RR, runs 4.82 miles under the Berkshire Mountain range, and took 22 years to complete. Work was begun in 1851 and the first train ran through in 1875. In 1870 dollars, it cost over $21-million, is over 25,000 feet long, took 500,000 lbs of nitroglycerine, excavated 2-million tons of rock and cost the lives of nearly 200 workmen. It is still the longest transportation tunnel east of the Rocky Mountains. The tunnel was electrified in early 1911 to eliminate the problem with smoke from steam engines.
The tunnel remained electrified until 1946, when the use of diesels made the electrics unnecessary. (Further information can be found in "A Pinprick of Light: The Troy & Greenfield Railroad and Its Hoosac Tunnel" by Carl R. Byron)