| Elevation in feet above pool level of under side of bridge over 360´ channel. | Present | 37´ | 42´ | 47´ | Present | 37´ | 42´ | 47´ |
|---|---|---|---|---|---|---|---|---|
| [33]Maximum gradients | Amount of rise in feet above Duquesne Way | |||||||
| Sixth Street bridge | 2.3% | 3.2% | 4.5% | 5.8%[34] | 7.5 | 10.4 | 15.4 | 20.4 |
| Seventh Street bridge | 3.0% | 3.7% | 5% | 6.3%[34] | 10.0 | 14.2 | 19.2 | 24.2 |
| Ninth Street bridge | 2.8% | 3.5% | 5% | 6.5%[34] | 10.1 | 13.3 | 18.3 | 23.3 |
| 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[35] 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.[36] 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 crossings will sooner or later alter the existing approaches in such a manner that the resulting gradients would not be further increased by raising the bridges. It is to be noted, however, that the precise elevations recommended by the local office of the United States Engineers for these bridges would involve serious complications with the railroad tracks.
In many cities having similarly situated level business and manufacturing districts along rivers, very large sums of money have been spent to reduce the gradients on the connecting bridges to less than 3 per cent, and that figure is rather generally regarded by engineers as a maximum upon important traffic bridges.
People in Pittsburgh are so accustomed to steep gradients in the adjacent hill districts that they are apt to ignore the fact that there is a city within their city, and that this inner manufacturing and business city is closely confined to the long drawn-out, irregular, level river-bottoms and is much freer from hills than New York, almost as much so as Chicago.
The city has expressed its willingness to spend a large sum of money and undergo great inconvenience for the sake of a moderate reduction in the street gradients of the "Hump" at one of the gateways of the hill districts. Important as this work is, it cannot be compared for a moment as a matter of traffic improvement with the importance attaching to easy gradients on the bridges, for the streets of the "Hump" district lead in the main from the flat part of the city to the hilly part where average loads are limited by the prevailing steep gradients, whereas the bridges lie between two parts of the level industrial and commercial city. If at low gradients they serve to unite them; if at high gradients they divide them.
Railroad Bridges.—In so far as any changes in the railroad bridges produce conditions less convenient and expeditious for handling the business which the people have to do with the railroad, the public has a direct concern in the matter.
With regard to the Junction Railroad bridge of the Baltimore and Ohio Railroad System, the raising proposed by the local office of the United States Engineers, appears to involve no serious difficulties in operation which would affect the general public or the shippers.