From these and many other illustrations that could be given it is evident that it is not universally or even commonly considered necessary or advisable to sacrifice business interests crossing the bridges to navigation interests using the waterways, to any such extent as that demanded by the navigation interests of the Allegheny River.
Conclusions as to Clearance Heights.—Disregarding for the moment the question of the time when changes in the present bridges should be required, it is believed, after very careful consideration, that the conditions brought out by our study of the problem would best be met by fixing the elevation for a substantial portion of each bridge in the center at a clear height above the pool level of substantially 37 feet, or 28 feet above the river at a 15-foot stage at each bridge. It is believed that this elevation will give fair, justifiable and all really needed accommodations to the navigation interests. This height can be attained without extravagant and unjustifiable expense and inconvenience to the business interests involved in crossing the river, and while it cannot be hoped that it would be satisfactory to the extreme advocates of river and harbor interests, it ought to satisfy those who are able and willing to give proper and fair consideration to other interests than their own. There are no reasonable navigation demands, with bridges at this elevation, that cannot be met if the water-borne commerce be conducted with vessels of the best modern accepted type and not of extreme or unnecessary height.
Piers and Channels.—For the benefit of the navigation interests there are certain changes in some of the bridges over the Allegheny that should be made without question. These relate to the location of piers and location and width of the navigable channels.
Bridges over the Seine, Paris, showing low clearance heights required and shallow water
At the extreme mouth of the Allegheny River a new bridge, the North Side Point bridge, has been approved by the War Department and is to be built. This is to have one central pier dividing the river into two channels.
A short distance above this North Side Point bridge is situated the Sixth Street bridge, in some respects the most important highway structure crossing the river. This bridge now corresponds to the North Side Point bridge in having a central pier and dividing the river into two main channels of ample width of over 400 feet.
The next bridge, the Seventh Street bridge, also has now a central pier with channels about 320 feet width on each side of it. The next bridge up the river, that at Ninth Street, has shorter spans, with the piers so unfortunately located as to be decidedly obstructive. As this bridge is of relatively light construction it is possible that the heavy and constantly increasing traffic which it is called upon to bear will before long necessitate its reconstruction anyway, and it will not be unreasonable to require it to be rebuilt with fewer piers properly located to conform to the plan adopted for the Sixth Street and Seventh Street bridges.