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With regard to the Pittsburgh, Fort Wayne and Chicago bridge of the Pennsylvania System, it is to be noted that this is a double-deck bridge, the upper tracks being used principally by passenger trains and the lower tracks by freight trains almost exclusively devoted to local freight business. The most serious consideration affecting this bridge is that any very considerable raising of the level of the lower tracks would throw them out of connection with the important local freight station to which those tracks run. Even if expense of reconstruction be wholly disregarded we believe no way can be devised by which the freight tracks of the Fort Wayne bridge, if raised as proposed by the local office of the United States Engineers can be connected with the freight station and industrial plants without involving greatly increased difficulty and delay in the handling of freight either on the tracks or in the station itself or in the teaming approaches to the station. When the large volume of local traffic handled at this station is considered, it is apparent that such a radical change is a serious matter for shippers and the great manufacturing and commercial industries of the city. Other than the expense of making changes in the bridge and its approaches no serious difficulty stands in the way of raising the clearance of the main span of the Fort Wayne bridge 2 or 3 feet to about 37 feet above pool level. To go above that figure involves the serious objections discussed above.

(b) Effect of Different Bridge Heights Upon River Traffic. -- The effect upon river navigation of any standard that may be adopted for the heights of bridges depends upon the heights of the vessels using the river and the fluctuations of the river level itself. (See Diagrams 4 and 5.)

By means of Davis Island Dam in the Ohio River the water of Pittsburgh harbor is now kept practically at a minimum stage of six feet above the datum of zero at natural low water. This is the prevailing water level for the greater portion of the year. Floods come occasionally, produced by rains and melting snows, and, of course, with the floods come increased current velocities. These current velocities of each river depend upon the source of the flood. When the flood comes down the Allegheny River high velocities result. When the flood comes down the Monongahela the high water in the Allegheny is back-water without excessive

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Last modified on 22-Dec 1999
Design format: copyright 1997-1999 Bruce S. Cridlebaugh
Original document: Frederick Law Olmsted, 1910