Dubuque Highway Bridge.—The highway bridge across the Mississippi River at Dubuque is an enterprise which came to its initial construction focus in 1886.
The contract was let to Mr. H. E. Horton, the lowest bidder, at $125,000, for the entire structure. Work was commenced and the first pile for the foundation driven September 17, 1886, and the celebration of its completion and opening for pedestrians and teams was held November 29, 1887. It is the longest crossing of its kind in the West and exclusively highway in character.
The following description is furnished by Mr. Tschirgi, jr., the engineer:
The bridge rests on seven piers; substructure of masonry, founded on piles, having an iron superstructure involving an 18-foot roadway and a walk 5 feet wide on each side. Four spans 205 feet long and one 248 feet appertain to that part of the bridge west of the channel span. The grade over these spans and the 248-foot span east of the channel span is 4 feet in 100. The cantilever channel span is 363 feet in length, leaving each end 50 feet in the clear above extreme high-water mark, while the center is 55 feet above, thus affording ample head-room for steamers. The main bridge is reached on the east end, or Illinois shore, by means of a solid approach, constituted partly by embankment with retaining wall and partly by excavation in the side of the stone bluffs, along a distance of 800- feet, thence by two iron spans, similar to those of the main bridge, each 120 feet long, forming a viaduct over the tracks of the Illinois Central Railroad and Chicago, Burlington and Northern Railroad. The length of the main bridge is 1,760 feet, and the approach 1,040 feet, making the entire length 2,800 feet. The location directly across the river is 75 feet below the Dubuque and Dunleith Railroad Bridge, the draw of which swings under the cantilever span of the high bridge. The channel piers Nos. 3 and 6 are 72 feet high above the grillage foundations. Construction throughout is according to plans and specifications approved by the best engineers in the country, all material being rigidly inspected and tested.