FREE INSTITUTE OF SCIENCE 



29 



THE ELIMINATION OF GRADE-CROSSINGS IN CITIES 



generally forms the masonry support is another decided improvement. The 

 engineer and the architect must work together in all such designs. 



There are a few details of the construction of the bridges required either 

 for the railroads or the streets which are important. Sufficient depth must be 

 provided to give a satisfactory floor construction. This must be about four 

 feet. It is necessary to cover the floor of a railroad bridge over a street in a 

 city with solid construction, so as to make it waterproof and prevent drippings 

 onto the street beneath and also to allow standard track construction of ties 

 and ballast to prevent undue noise. It is also advisable to protect the under- 

 side of a floor of a bridge of a street over a railroad so as to prevent corrosion of 

 the metal from the fumes of the locomotive. In the State of Pennsylvania 

 the clearance from a street to the underside of a railroad bridge crossing it 

 must be at least fourteen feet. When a street crosses railroad tracks the Pub- 

 lic Service Commission is insisting on a clearance of twenty-two feet when it 

 can be possibly obtained, and this is also good railroad practice. 



7. TWO TYPICAL EXAMPLES OF WORK IN PHILADELPHIA 



Our own city furnishes two interesting cases of grade-crossing elimination 

 which it may be profitable to compare. They are: First, the Subway and 

 Tunnel on Pennsylvania Avenue on the Reading System, and second, the so- 

 called Elevated on Ninth Street and through the Tioga district on the same 

 system. 



ist. On the Pennsylvania Avenue Subway seventeen grade-crossings 

 were eliminated, including important ones at Broad Street and at the Spring 

 Garden entrance to Fairmount Park. The work covered a distance of two miles, 

 generally of tracks depressed beneath the surface of the streets in an open sub- 

 way and a tunnel. Travel was largely diverted during construction to other 

 lines or to adjacent streets. An entirely new system of sewers was necessary, 

 involving a cost of about $500,000. All yards and other railroad facilities were 

 depressed. The total estimated cost was $6,000,000, and the actual cost, in- 

 cluding all consequential damages, was $5,500,000. This cost was divided 

 evenly between the city and the railroad company. The work represents a 

 cost of $2,750,000 per mile of structure. Generally there are four tracks. The 

 time consumed in construction was about five years. 



The work was planned in 1894, and the ordinance of councils authorizing 

 its construction was passed on March 17th of that year. At that time the 



