When completed the Hoosac Tunnel measured 20' Tall and 24' Wide with a base of 23'. Just as it was originally contracted. It has a grade of 26 2/5 feet per mile heading towards the center. This pitch is there to allow water to flow out without the need for pumping.
For those interested, the actual geologic composition of the mountain is (from east to west):
- Rowe Schist
- Stamford Granite Gneiss
- Metamorphic Conglomerate
- Hoosac Schist
- Stockbridge Limestone