As a permanent arrangement of piers for the above three bridges either of two logical plans may be adopted. The first is to retain the existing two-spans center-pier arrangement of the Sixth Street and Seventh Street bridges, conforming to the center pier plan required by the United States Engineers for the new North Side Point bridge, and reconstruct the Ninth Street bridge upon the same general plan. The other is to reconstruct all three bridges with two piers and three spans each, as recommended by the local office of the United States Engineers. The first or central pier plan has the merit of economy of construction in that it involves the construction of no new piers for the Sixth Street and Seventh Street bridges, and permits the continued use of the existing superstructures of the Sixth Street and Seventh Street bridges by simply raising them to the elevation that may be decided upon and ordered. So far as we can ascertain, in view of the center pier plan adopted for the North Side Point bridge, the advantage to navigation appears to lie on the side of adhering to a center pier plan for these bridges also. On the other hand, there is no doubt that three-span bridges could be made more agreeable in appearance than two-span bridges. But the possible gain in appearance alone does not appear sufficient to justify the adoption of three spans.
The next bridge above Ninth Street is that of the Pittsburgh, Fort Wayne and Chicago Railroad. This has been constructed with two main piers providing one main central channel 337.5 feet wide and three other piers giving four channels from 155 to 163 feet wide. Owing to the bend in the river at the bridge and the distance above the Ninth Street bridge, there is no valid objection to this single main central channel at the railroad bridge connecting either with two channels divided by the central piers of the bridges below, or with a central channel if those bridges should be reconstructed on the three-span plan.
Paris bridges and boats—low boats to fit bridges
The Sixteenth Street bridge has been constructed with 3 piers dividing the river into 4 channels of about 150 feet each; the clear head room beneath it is less than that now given by the bridges below it. The best arrangement to be made with this bridge is to require it to be rebuilt without the central pier, leaving a central channel about 320 feet in width between the two side piers to correspond with the railroad bridge just below it. It is an old, covered, wooden bridge, in poor physical condition, and, as previously noted, it is probable that it must be raised anyhow in connection with eliminating railroad grade crossings on the approaches.
The Thirtieth Street bridge has its piers properly spaced to leave a central channel 285 feet in clear width and no changes are required in pier and channel location at this bridge.
The Thirty-third Street or Pittsburgh Junction Railroad bridge of the Baltimore and Ohio System has 3 piers, giving a main central channel of 232 feet wide, with side channels 195 feet wide, and on the Herrs Island side of 150 feet. No change is needed in the location of the piers and channels at this bridge.
The Forty-third Street bridge is built with 3 piers, making 4 channels each of about 160 feet wide. It gives less clear head room at high river stages than most of the lower river bridges. It is an old wooden bridge, in poor physical condition. The best arrangement for this bridge is to treat it as the Sixteenth Street bridge, and to require it to be rebuilt, omitting the central pier and leaving a central channel about 300 feet wide, to correspond with the bridges below it. The elimination of railroad grade crossings on the approaches to this bridge is already a pressing public need and must soon result in its raising or reconstruction at a higher level.
Considerations against Requiring Changes in Bridges To Be Made at Present.—The following important questions, having a direct bearing upon the proper design of permanent bridges across the Allegheny River, are now under consideration: