The Hoosac Tunnel is a 4.75mi 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 8.5mi 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.The tunnel runs in a straight line from its east portal, along the Deerfield River in the town of Florida, to its west portal in the town of North Adams. It remains an active freight rail line, owned by Pan Am Railways and operating without a schedule. "No Trespassing" signs are posted throughout the area and it is illegal to enter the tunnel or walk on the railroad tracks without permission. The tunnel is frequently monitored by Boston & Maine Police. Trespassing in the tunnel or on railroad property may result in arrest, injury, or death.