Where did the tunnel trains get their power from?
Commonwealth Edison supplied the electricity and the Chicago Tunnel Company maintained four substations to convert the electricity to 250 volts direct current for powering the trains, elevators, and lights. Like streetcars on the surface, the trolley wire was positive and the rail was the negative ground. Because the energized trolley wire was only about six and a half feet above the rails, special care had to be taken to avoid electrocution. This was especially critical while sitting on a metal locomotive, standing in a metal car, or standing in a puddle of water. Some buildings built special wooden guards around the trolley wire in their basements to help workers avoid electrocution while loading and unloading cars. This early postcard view shows a test train passing through an intersection on third rail cog tracks. The one foot gauge track in the right foreground was used during construction to remove clay excavations with small mine cars. A brass plaque in the center of the photogr
