The Chicago Tunnel Company was the builder and operator of a 2 ft narrow-gauge railway freight tunnel network under downtown Chicago, Illinois. This was regulated by the Interstate Commerce Commission as an interurban even though it operated entirely under central Chicago, did not carry passengers, and was entirely underground. It inspired the construction of the London Post Office Railway.
Under the streets of Chicago, pre-1906
Tunnel under construction in 1902. The freshly cut clay ahead of the concrete work shows clear knife marks.
Trackwork in a typical grand union where two tunnels intersected, photographed before 1906
Two Morgan Locomotives posed for a publicity photo in 1904 at State and Randolph. Superintendent George W. Jackson is at the controls on the left.
In transport, tunnels can be connected together to form a tunnel network. These can be used in mining to reach ore below ground, in cities for underground rapid transit systems, in sewer systems, in warfare to avoid enemy detection or attacks, as maintenance access routes beneath sites with high ground-traffic such as airports and amusement parks, or to extend public living areas or commercial access while avoiding outdoor weather.
Connecting tunnel under Ouvrage Michelsberg, a fortress of the Maginot Line
Part of the tunnel complex at Củ Chi, this tunnel has been made wider and taller to accommodate tourists.
The Structureplan of Vinh Moc Tunnels.
