Most underground terrestrial fiber optic cable infrastructure is only several feet below grade. However, there is one network in particular that is far deeper. Below the streets of Metropolitan Chicago is an extensive tunnel system that is about forty feet below the street level.
Originally licensed by the City in 1899 for telephone cables, the tunnel system was mostly used to move freight, coal, and mail throughout the city by small electric narrow gauge trains. Major commercial use of the tunnel system ended in the 1950s with the bankruptcy of the operator. Chicago’s Grant Park was expanded in the early 20th century with landfill, much of it from excavations of the tunnels.
A new use for the tunnels was initiated in the late 1980s with the development of the Competitive Local Exchange Carrier (CLEC), a telecommunications provider company created to compete with the incumbent telephone provider. Metropolitan Fiber Systems (MFS) was a CLEC that used the remaining tunnel system to build a fiber optic cable network.
I was a splicing technician working on the MFS project and it was one of the most unusual working environments of my career! The workday began by donning a hard hat equipped with a miner lamp and hip waders. We would elevator down to the basement stairwell, then down to a sub-basement, and then shimmy through a narrow opening punched through the concrete. After that, we laddered down through a narrow opening finally opening to the tunnels.
We hand-carried everything we needed for the workday, sometimes walking 10 to 15 city blocks to a splice location. Later a crew member acquired a folding trailer that would fit through the narrow opening, bringing much relief. Walking through the tunnels was like passing through a catacomb. Cool and damp with street names painted on tunnel intersections. The tunnels were close to 90 years old by this time and it was like traveling through a ghost town, remnants left behind of an age past.
On the morning of April 4, 1992, I received a call from the company splicer informing me that work had been halted because the tunnels were full of water! A piling driven too close to the tunnel had allowed the Chicago River to flood the tunnels. It was a major disaster for the city but the fiber network survived without major incidents. We did have to return weeks later after the water was removed to empty the splice closures which had not been sealed because we thought they would never be saturated.