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TABLE SHOWING EFFECTIVE ENERGY REQUIRED TO OVERCOME RISE OVER BRIDGES AT VARIOUS HEIGHTS

Elevation in feet above pool level of under side of bridge over 360' channel.		Present	37'	42'	47'
	Tons per annum	Foot tons of effective energy
Sixth Street bridge	13,240,010	99,300,075	137,696,104	203,896,154	270,096,204
Ninth Street bridge	14,732,130	151,740,939	195,937,329	269,597,979	343,258,629
			Per cent of increase of effective energy required
Sixth Street bridge			38.6%	105.3%	172.0%
Ninth Street bridge			29.1%	77.7%	126.2%

At the Sixth Street bridge there is at present an undesirably steep gradient* on the Allegheny, or North Side, approach, but it is only 230 feet long and being paved with stone gives a good foothold for horses. This is to be greatly benefited by filling up the street with material taken from the "Hump" grading, the plans on file in the City Bureau of Construction providing for an improved gradient of only 2.22 per cent. Many of the abutters have already waived their damages and there is no question that the improvement will be made. The present bridge gradients and those of the Pittsburgh approach are less than 3 per cent. At the Seventh Street bridge the gradients do not exceed 3 per cent, except on the Allegheny approach where it is now being reduced to 2 per cent. At Ninth Street, while the present bridge gradients do not exceed 2.8 per cent, there is a short pitch about 100 feet long in the approach on the Allegheny side with a grade of 5.24 per cent.** A small amount of regrading, involving no heavy property damages, will suffice to reduce these gradients to 1.3 per cent, and appropriations for this improvement have already been made by the City.

The existing grades at the Sixteenth Street, Thirtieth Street and Forty-third Street bridges are light, but it is not important to consider these bridges in detail in this connection as it is probable that the necessity for eliminating railroad grade

*3.64 per cent (United States Engineers, Office) or 4.0 per cent. (City Bureau of Construction.)

** Given as 6.35 per cent on United States Engineers' Sections.

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