electrification. Operation began in 1895 with three General Electric locomotives. These locomotives only worked pulling northbound trains; southbound traffic simply coasted through this section, which was all downhill. Initially the system used a unique overhead track in which the current shoe rode, but shortly after it was converted to a conventional third rail system. The electrification was discontinued in 1952 when dieselization made it unnecessary. Boston & Maine Railroad (Hoosac Tunnel) The Hoosac Tunnel was electrified by the Boston & Maine Railroad in May 1911. This was done to speed up trains and to reduce smoke in the tunnel. Electricity was provided from the Zylonite power plant in Adams, MA. The electrification was switched off in August 1946 with the arrival of diesel locomotives on the route. Grand Trunk Railway (St. Clair Tunnel) The St. Clair Tunnel is the name for two separate rail tunnels which were built under the St. Clair River between Sarnia, Ontario and Port Huron, Michigan. It was the first full-size (i.e. able to allow a railroad to run through it) subaqueous tunnel built in North America. Steam locomotives were used in the early years to pull trains through the tunnel, however concerns about the potential dangers of suffocation should a train stall in the tunnel led to the installation of catenary wires for electric-powered locomotives by 1907. The first use of electric locomotives through the tunnel in regular service occurred on May 17, 1908. The electric-powered locomotives were retired in 1958 and scrapped in 1959 after CNR retired and scrapped its last steam-powered locomotives on trains passing through the tunnel. New diesel-powered locomotives did not cause the same problems with air quality in this relatively short tunnel. Great Northern Railway (Cascade Tunnel) The Great Northern Railway (now BNSF Railway) electrified the original Cascade Tunnel in 1909, near the summit of Stevens Pass in the Cascade Mountains. This first electrification system with GE-built boxcabs were the only three-phase AC power ever used on North America railroads, see Three-phase AC railway electrification. The electric boxcabs pulled trains through the tunnel with their steam locomotives still attached until they were retired in 1927. In 1925 work began on the new Cascade Tunnel, with the Great Northern ultimately electrifying a section of its main line route to Seattle, Washington from Wenatchee to Skykomish. The new tunnel and electrification reduced the mainline by , eliminated of elevation and of snow