Passing through

The Metropolitan Bridge on the Chicago River with The Pueblo passing through the open span in 1907

Metropolitan West Side Elevated Railway Bridge was used for electric trains from 1895 until 1958. This was the only 4 track bridge in Chicago’s history.

Most sites seem to call it a Jackknife bridge for some reason however, this is clearly a Chicago Type, Double Leaf, Trunnion, Bascule Bridge. This description can be broken down as follows:
– Chicago Type describes a design that evolved from research done in the late 1890’s by the Chicago Bridge Department to find a patent free design that would accommodate both land and water based traffic;
– These bridges rotate vertically about trunnions (axles) on the river bank;
– A leaf is the portion of the bridge deck that spans the river. All of these bridges use two leaves to span the river – thus Double Leaf;
– Bascule describes a family of draw bridges that use counterweights to assist in the vertical movement of bridge leaf.