o TRANSACTIONS OF WAGNER 



28 



THE ELIMINATION OF GRADE-CROSSINGS IN CITIES 



them both economical and esthetic, but because it is difficult it should not be 

 overlooked. 



There is no class of bridge structure that is more pleasing to the eye than 

 an arch of masonry, nor more lasting and satisfactory from the standpoint of 

 maintenance, and if sufficient height can be obtained from rail to street, or 

 vice versa, without too much cost, the arch should be used. In any extended 

 piece of crossing elimination involving a number of adjacent crossings it is 

 very difficult to obtain sufficient headroom for an arch without resulting in a 

 practically prohibitive cost, and generally some form of steel or reinforced con- 

 crete construction of the plate girder or flat slab type has to be used. 



When such construction has to span a wide street or a number of tracks, 

 it becomes necessary to provide a number of intermediate supports in order to 

 design a structure with sufficient strength with a moderate depth. For many 

 years cities would not allow any such intermediate supports except along the 

 curb lines of the streets. If the driveway of the street was wide, this made it 

 necessary to provide a steel girder, or even a truss of such depth as to be de- 

 cidedly unsightly. Recently a decided movement for the improved appear- 

 ance of such structures has developed by allowing supports to be placed in the 

 middle of the driveways, as well as along the curb Hnes. This makes it possible 

 to reduce the depth of the structures so that no part of them is above the top 

 of the rail of the tracks. This provides a safety condition, as far as the railroad 

 is concerned, in removing obstructions which are dangerous to trainmen. The 

 supports in the middle of the driveway are no longer dangerous to vehicular 

 traffic in the streets when one considers that when traffic has to be regulated 

 a poHceman is placed in the middle of the street, to keep each Hne of traffic on 

 its proper side. The case of the Pennsylvania Railroad crossing over Broad 

 Street, Philadelphia, at the North Philadelphia Station, where the supports 

 are in the center of the driveway, is of this kind, and no one would for a 

 moment consider that they were objectionable. 



If it becomes necessary to place steel girders over a street, it is much better 

 to arrange the details so as to allow the girders to show, and treat the whole 

 structure architecturally, than to attempt to cover the steel with ornamental 

 work of some kind. A splendid example of this kind of treatment is the Chest- 

 nut Hill Branch of the Pennsylvania Railroad crossing Allegheny Avenue, in 

 Philadelphia. The painting of steel girders to match the concrete which 



