WEST OF S WESTERN AVE, SOUTH OF 31ST ST

"EIGHT-TRACK" BASCULE BRIDGE

DESIGNED IN 1901 AS A CROSSING OVER THE CHICAGO DRAINAGE CANAL, THIS BRIDGE WAS USED BY 3 DIFFERENT RAILROAD COMPANIES: THE PITTSBURG, CINCINNATI, CHICAGO, AND ST LOUIS RAILROAD, THE CHICAGO AND NORTHERN PACIFIC RAILROAD, AND THE UNION STOCK YARDS AND TRANSIT COMPANY. THE FIRST PROPOSAL WAS A MASSIVE SWING BRIDGE, BUT THE COMPANIES WERE CONCERNED THAT IF ONE OF THE NECESSARY EIGHT TRACKS WAS DAMAGED, IT WOULD SHUT DOWN TRAFFIC FOR ALL LANES. THE SCHERZER ROLLING LIFT BRIDGE COMPANY WON THE CONTRACT WITH ITS SOLUTION OF FOUR SEPARATE PARALLEL DOUBLE-LEAF SPANS. THESE THREE-HINGED THROUGH-TRUSS STRUCTURES WERE THEN REPLACED, IN ACCORDANCE WITH A 1909 SANITARY DISTRICT DEADLINE FOR THE REMOVAL OF ALL FIXED SPANS OVER THE DRAINAGE CANAL, BY THE NEW SINGLE-LEAF ROLLING LIFT BRIDGES ERECTED BY CHICAGO BRIDGE AND IRON WORKS.

THE FOUR BRIDGES' COUNTERWEIGHTS ALTERNATE BETWEEN NORTH AND SOUTH, REDUCING COMPRESSION ON THE PIERS AND MAKING MORE ROOM FOR OPERATING MACHINERY. THIS UNIQUE DESIGN ALSO CREATES A NESTED, TRIANGULATED SYMMETRY.

TODAY THE SPANS HAVE BEEN FIXED AGAIN AND HAVE THE LOWEST VERTICAL CLEARANCE ANYWHERE ON THE SANITARY CANAL, 16 FT.

SOURCE:

LIBRARY OF CONGRESS: HISTORIC AMERICAN ENGINEERING RECORD: "PENNSYLVANIA RAILROAD, "EIGHT-TRACK" BASCULE BRIDGE"
HAER No. IL-99