The Hoosac Tunnel (also called Hoosic or Hoosick Tunnel) is a 4.75-mile (7.64 km) active railroad tunnel in western Massachusetts that passes through the Hoosac Range, an extension of Vermont's Green Mountains. Work began in 1851 with an estimated cost of $2 million and ended in 1875 with a total cost of $21 million. At its completion, the tunnel was the world's second-longest, after the 8.5-mile (13.7 km) Mont Cenis Tunnel through the French Alps. It was the longest tunnel in North America until the 1916 completion of the Connaught Tunnel under Rogers Pass in British Columbia, and remains the longest active transportation tunnel east of the Rocky Mountains.