Chicago Type, Double Leaf, Trunnion, Bascule Bridge

The complete title of these bridges is "Chicago Type, Double Leaf, Trunnion Bascule Bridge." While quite a mouthful, this description can be broken down as follows:

There are four eras or generations of the Chicago Type bridge in Chicago. Three of these generations are represented in these eighteen bridges.

First Generation (1902-1910 -- none of the eighteen):

Distinguishing Features: Three Through Trusses; rack and pinion on the outside of the truss. (example shown below is the single leaf bridge at W. Kinzie St. spanning the North Branch of the Chicago River- photo taken looking west from N. Orleans St.)

Second Generation (Beaux Arts - 1910-1930, twelve of the eighteen)

Distinguishing Features: Two Trusses; rack and pinion moved to the inside of the truss; variable truss designs; ornate bridge tender houses, railings, staircases, etc. (examples shown below are N. La Salle and N. Clark St. bridges)

Third Generation (Art Deco - 1935-1950, two of the eighteen)

Distinguishing Features: Similar to Second Generation with less ornamentation. (example shown below at N. State St.)

Fourth Generation ("Modern" -- four of the eighteen)

Distinguishing Features: Single bridge tender house; No ornamentation. (example shown below at N. Dearborn St.)