Chapter XI: Introduction

March 15th, 1910, upon recommendation of the Committee on City Planning, the Pittsburgh Civic Commission authorized Colonel Thomas W. Symons, Corps Engineers, U. S. A. retired, and Mr. Frederick Law Olmsted to make a report upon desirable heights and pier locations for bridges over the Allegheny River. The purpose of the Commission was to secure a report which weighed the interests of all parties to the bridge question, and which would strike a balance to meet the various transportation needs of Pittsburgh.

The Commission asked the Committee on City Planning to direct the preparation of the report. The Committee consists of T. E. Billquist, chairman; Charles F. Chubb, H. J. Heinz, Benno Janssen, Richard Kiehnel, E. K. Morse. This committee passed upon the report April 18th and recommended it to the Commission for adoption. On April 25th the Commission received and adopted the report and voted their hearty appreciation of the work of Colonel Symons, Mr. Olmsted and the Committee on City Planning. This report was published separately in May 1910.

RECOMMENDATIONS

1. That the Sixteenth Street and Forty-third Street bridges, which are obstructions to navigation on account of their pier locations, narrow channels, and exceptionally low clearance height, be required to be rebuilt with their piers so located as to give channels conforming to the neighboring bridges, and that their elevation be fixed with regard to eliminating the railroad grade crossings on their approaches, but the minimum clearance shall be fixed in accordance with the closing paragraph below.

2. That the Ninth Street bridge should be rebuilt as soon as practicable with a central pier and two wide spans conforming to those of the Sixth Street and Seventh Street bridges. The design of the new Ninth Street bridge, however, should not be finally determined and erection begun until a definite plan for comprehensive improvements in the traction system between the two sides of the river has been decided upon. Unless new circumstances develop before the construction of this bridge is begun that materially affect the problem of clearance height, the elevation should be fixed in accordance with the closing paragraph below.

3. That all questions pertaining to changing the elevation of the Sixth Street, Seventh Street, Fort Wayne, Thirtieth Street and Junction Railroad bridges be deferred to await the report of the Pittsburgh Flood Commission and the resultant action; to await the report on a comprehensive plan for traction improvements; to await the completion of the work projected by the City in cutting down some streets and filling others; and to await the results of the investigation of river boat design and construction provided for in the River and Harbor bill just passed by Congress.

4. That if it is deemed essential and necessary at present to decide upon the elevation to which all Allegheny River bridges must be made to conform, this elevation be fixed so that there shall be a clear head room of substantially 37 feet above pool level, varied so as to give at each bridge a clear head room of 28 feet when the river is at a 15 foot flood stage. This height to be maintained over the entire main span where there is a central span and for 180 feet on each side of the central pier where there is a central pier.

FULL REPORT

April 19th, 1910

THE PITTSBURGH CIVIC COMMISSION:

_Gentlemen_: In accordance with your expressed desire we have examined into the bridge problem on the Allegheny River now before the City, particularly in regard to the use of the bridges and their connections with the streets of the city and the use of the river for harbor and navigation purposes, and beg to submit the following report thereon:

There are three great interests concerned in the problem of the bridges over the Allegheny River at Pittsburgh: (1) those who frequently cross the river or whose business requires the transportation of workmen, raw and manufactured material, and supplies from one side of the river to the other; (2) those concerned in the navigation of the river and harbor, and (3) those who own and operate the bridges.

In the hearings recently held on the subject much consideration has been given to the bridge owners and the navigation interests but comparatively little attention has been given, at first hand, to the interests of the general public, who in great numbers are interested in transportation across the river and for whose service both the bridges and river transportation exist.

It is quite apparent, from a study of the situation and the interests involved, that changes might be demanded in the bridges which would give some added advantage to river navigation, but yet would place so great a burden upon the interests concerned in crossing the river that the result would be a net loss to the general public. The following are the two extreme positions somewhere between which all concerned would agree that a balance of interests most beneficial to the general public must be determined:

From the viewpoint of traffic across the river the best arrangement would be level bridges at the grade of the connecting streets, regardless of river traffic. The more bridges are raised above that standard, apart from any question of first cost, the greater will be the interference with travel across the river, up to the point of prohibitive grades on the bridges and their approaches. Before this point is reached drawbridges must be considered which, while often required and adopted, are objectionable to the interests using the bridges and those passing under or through the bridges.

From the viewpoint of the river interests the most complete improvement would be to do away with the bridges entirely, thus giving absolute freedom of navigation. This is out of the question. The next best thing from that point of view would be to change the bridges to one span each across the river from bank to bank with height enough for passage beneath of the highest floating structures at all stages of the river. This would be impracticable without remodeling the city along both sides of the river for long distances from the banks at an expense so great as to be almost beyond computation. Anything less than this will impose, at least in theory, some hindrance upon river navigation, and this hindrance will be greater in amount as the head room is decreased and as piers are introduced into the river.

The aim in arriving at a solution of the bridge problem must be to adjust these conflicting interests impartially; and the factors to be considered in arriving at such an adjustment are these: _First_, the amount and importance of the traffic likely to be affected in each case. _Second_, the extent to which any given solution would benefit or injure the bridge traffic and the river traffic, respectively.

1. _Amount and Importance of Traffic Affected._--_(a)_ _Bridge Traffic_.--There are in question six highway bridges and two railroad bridges.

UNDER BRIDGES OVER BRIDGES
--+---------+---------------+----------+------------------------------------
TONNAGE IN MILLIONS
██|2,344,398| SIXTH ST. |13,240,010|████████
██|2,796,122| NINTH ST. |14,732,130|█████████
█|2,228,270| FT. WAYNE. |53,127,210|████████████████████████████████████
▐|1,045,570| THIRTIETH ST. | 398,430|▎
▐| 865,024| JUNCTION RR. |24,335,982|████████████████▌
▐| 714,856|FORTY-THIRD ST.| 311,090|▎
--+---------+---------------+----------+------------------------------------
PASSENGERS IN MILLIONS
▕| 25,680| SIXTH ST. |27,098,291|████████████████████████████████████
▕| 30,567| NINTH ST. |24,325,900|████████████████████████████████▌
▕| 24,408| FT. WAYNE. | 4,877,495|██████▌
▕| 11,455| THIRTIETH ST. | 715,985|█
▕| 9,475| JUNCTION RR. | 217,254|▎
▕| 7,831|FORTY-THIRD ST.| 816,333|█
--+---------+---------------+----------+------------------------------------
UNDER BRIDGES OVER BRIDGES

Diagram No. 1, showing comparative importance of traffic over and
under Allegheny river bridges

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| | 108,000,000 TONS | |
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| +----------------------------------------+ |
| OVER BRIDGES |
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| +----+ |
| 1,500,000 |
| TONS |
| UNDER |
| BRIDGES |
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| COMPARATIVE DIAGRAM SHOWING TOTAL TONNAGE, OVER AND UNDER THE |
| ALLEGHENY RIVER BRIDGES. |
| |
| TO ACCOMPANY REPORT OF |
| COL. THOMAS W. SYMONS. |
| FREDERICK LAW OLMSTED. |
+------------------------------------------------------------------+

Before referring to the statistics in regard to traffic over these bridges we wish to point out that much the greater part of it is of a kind daily and intimately affecting the business and the convenience of a large population. Any delay affecting the transportation of passengers over any of these bridges, and any delay or any increase of cost in teaming package freight and supplies from freight stations and warehouses and stores on one side of the river to their destination on the other side, would be felt very sharply by a considerable fraction of the manufacturers, merchants and other citizens of Pittsburgh. The inconvenience arising from any interference with traffic of this class would clearly be greater in proportion to the volume and value of the traffic than in the case of the slower moving river traffic. Ten minutes' delay to people in reaching their offices or an hour's delay beyond the expected time in the delivering of household food supplies or express packages, etc., for a number of families, is a much more serious matter than a corresponding or even a greater delay in the delivery of a barge-load of gravel or coal, even though the barge-load were of equal value with the delayed lot of supplies.

Details in regard to the volume of traffic over the bridges and estimates of the value of the goods transported and the equipment engaged in the traffic are given in Appendix I and are summarized in graphical form in Diagrams 1, 2 and 3. The amount and importance of bridge traffic may be summarized by stating that there passes over the existing Allegheny River bridges each year about 108,000,000 tons of traffic roughly valued at $9,350,000,000; and about 62,700,000 human beings, passengers and pedestrians.

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| | $9,366,973,935 | |
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| +---------------------------------------------+ |
| OVER BRIDGES |
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| +----+ |
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| +----+ |
| $105,000,000 |
| UNDER |
| BRIDGES |
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| COMPARATIVE DIAGRAM SHOWING TOTAL VALUE OF TRAFFIC OVER AND |
| UNDER THE ALLEGHENY RIVER BRIDGES. |
| |
| TO ACCOMPANY REPORT OF |
| COL. THOMAS W. SYMONS. |
| FREDERICK LAW OLMSTED. |
+------------------------------------------------------------------+

_(b)_ _River Traffic._--The data in regard to existing navigation under the Allegheny bridges consist of detailed reports of vessels and cargoes passing Dam No. 1 and counts of the number of vessels passing under the several bridges during representative periods of from one to two months in 1909. From these data we have estimated the annual river traffic under each of the bridges, and very roughly, its value.[32] These amounts are shown graphically in comparison with the corresponding figures for traffic over the bridges in Diagrams 1, 2 and 3. To briefly summarize, it may be stated that the river traffic of the Allegheny River in one year amounts in the aggregate to about 3,500,000 tons, including all freight carriers and power boats, roughly valued at about $105,000,000; and about 35,000 human beings, passengers by boat.

It seems well here to note that the water-borne traffic of the Allegheny River has been steadily decreasing for many years and is now but a small portion of that which once existed. That this decline in river traffic is not due to the interference of the bridges is shown by the statement that the navigation facilities are better than ever before. It is due to the lack of modern terminal facilities, boats and methods of carrying on business.

There is a possibility that, in case improved conditions are provided for Allegheny River navigation, the amount thereof may increase with the lapse of years, but for the reasons set forth in Appendix II, this increase is not likely to be so great in relation to the natural increase of the bridge traffic as to render the comparison of the existing facts in Diagrams 1, 2 and 3 inapplicable to the future.

_(c)_ _Comparison of Bridge and River Traffic_.--To sum up, it may be said that each year the amount of traffic passing over the bridges is at least 30 times that floating on the water of the river, and about 90 times its value. The passenger traffic over the bridges is about 1800 times that on the water. The character of the traffic over the bridges is such that a given degree of interference with it is a far more serious annoyance to the public than the same degree of interference with river traffic.

2. _Effect of Various Solutions._--It remains to be considered to what degree the bridge traffic and the river traffic would be hampered or facilitated by various permanent solutions of the bridge problem. With a view to arriving at a plan as nearly ideal as the circumstances permit for a permanent arrangement of bridges over the Allegheny River, various projects have been put forward and considered. These concern two nearly independent matters, the elevation of the bridges above pool level and the location and design of the bridge piers. The former must be decided with regard to the effect upon both bridge and river traffic; the latter may be determined with regard solely to the navigation interests, giving due consideration to the cost and the appearance of the resulting bridges, as discussed below.

The plan upon which interest is now most centered is that officially recommended by the local office of the United States Engineer Corps. We shall consider the effect of the bridge heights proposed in this plan as compared with certain modifications thereof; first, upon the bridge traffic, and second, upon the river traffic.

_(a)_ _Effect of Various Possible Bridge Heights upon the Traffic over the Bridges_.--_Highway Bridges._--The highway bridges carry two principal classes of travel. The first consists of vehicles moved by power, electric cars and automobiles, and of pedestrians. With this class an increase of gradient on the bridges or their approaches, within reasonable limits, simply means the expenditure of a moderate amount of additional energy without material loss of time, or other difficulties. The second class consists of horse-drawn vehicles a large portion of which do not enter the hill districts but are limited in their movements to the large district lying on the lowlands of the three river valleys or accessible therefrom on moderate gradients. A great deal of this teaming consists of freight of all kinds received or shipped at the numerous freight stations on both sides of the river. The area accessible on roads of easy gradient from each end of these bridges is very great and includes nearly all the important industrial plants in Pittsburgh as well as all the freight stations and the principal warehouses, retail stores and other commercial establishments of Pittsburgh and Allegheny. Any considerable increase of gradient on these bridges means a reduction in average size of load hauled by vehicles of this important class, and a corresponding increase in the number of trips and in the number of teams required to do the work, making for increased cost and greater congestion of traffic. For all horse-drawn vehicles an increase of gradient on the bridges, beyond a certain limit, means, especially in wet or snowy or frosty weather, more slipping and falling, more stalling of all bridge traffic by such accidents, more wear and tear on horse flesh, and a resultant increased burden on the people. To raise the gradient of the bridges from those now existing to those indicated in the plans of the local United States Engineers' office would more than double the traction effort required in hauling over these bridges.

It must be borne in mind that, as the gradients increase, the cost of teaming and the wear and tear on teams increases much more rapidly than the theoretical effective horse power, because of the increased difficulty of foothold. It is impossible to measure the effect of any given increase of grade with precision, but a comparison of the existing conditions with those resulting from various possible bridge heights will give a good general idea of the effect as shown by the following tables:

TABLE SHOWING BRIDGE GRADES INVOLVED BY THE ADOPTION OF
VARIOUS CLEARANCE HEIGHTS

----------------------+-----+-----+-----+---------+-----+-----+-----+-----
Elevation in feet | | | | | | | |
above pool level of |Pre- | 37´ | 42´ | 47´ |Pre- | 37´ | 42´ | 47´
under side of bridge | sent| | | | sent| | |
over 360´ channel. | | | | | | | |
----------------------+-----+-----+-----+---------+-----+-----+-----+-----
|[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
----------------------+-----+-----+-----+---------+-----+-----+-----+-----

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

=============================================================================== Elevation in feet | | | | | above pool level of | | Present | 37´ | 42´ | 47´ under side of bridge| | | | | over 360´ channel. | | | | | --------------------+ 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.

With regard to the Pittsburgh, Fort Wayne and Chicago bridge of the Pennsylvania System, it is to be noted that this is a double-deck bridge, the upper tracks being used principally by passenger trains and the lower tracks by freight trains almost exclusively devoted to local freight business. The most serious consideration affecting this bridge is that any very considerable raising of the level of the lower tracks would throw them out of connection with the important local freight station to which those tracks run. Even if expense of reconstruction be wholly disregarded we believe no way can be devised by which the freight tracks of the Fort Wayne bridge, if raised as proposed by the local office of the United States Engineers can be connected with the freight station and industrial plants without involving greatly increased difficulty and delay in the handling of freight either on the tracks or in the station itself or in the teaming approaches to the station. When the large volume of local traffic handled at this station is considered, it is apparent that such a radical change is a serious matter for shippers and the great manufacturing and commercial industries of the city. Other than the expense of making changes in the bridge and its approaches no serious difficulty stands in the way of raising the clearance of the main span of the Fort Wayne bridge 2 or 3 feet to about 37 feet above pool level. To go above that figure involves the serious objections discussed above.

_(b)_ _Effect of Different Bridge Heights Upon River Traffic_.--The effect upon river navigation of any standard that may be adopted for the heights of bridges depends upon the heights of the vessels using the river and the fluctuations of the river level itself. (See Diagrams 4 and 5.)

By means of Davis Island Dam in the Ohio River the water of Pittsburgh harbor is now kept practically at a minimum stage of six feet above the datum of zero at natural low water. This is the prevailing water level for the greater portion of the year. Floods come occasionally, produced by rains and melting snows, and, of course, with the floods come increased current velocities. These current velocities of each river depend upon the source of the flood. When the flood comes down the Allegheny River high velocities result. When the flood comes down the Monongahela the high water in the Allegheny is back-water without excessive currents. Under this condition the Allegheny becomes a harbor of refuge for Monongahela commerce; and the reverse is true that in an Allegheny River flood the Monongahela becomes a harbor of refuge for Allegheny commerce. The floods in the two rivers seldom come at the same time on account of the differences in the topography and climatic conditions along the two water-sheds. The most serious floods in the Allegheny generally come in the spring, when they are frequently accompanied with drift and ice to such an extent as to render navigation dangerous. At a stage of 15 feet in an Allegheny River flood the river current runs at rates of from 4 to 7 miles per hour. The record of fifty-five years shows that there is an average of 9 days each year when the river is above a 15-foot stage, and this is mostly in the winter and spring when navigation in the harbor is at its lowest ebb. There is presented herewith Diagram 4, showing graphically the average number of days each year during which the river has reached the various heights indicated.

There is also presented a hydrograph record of the river for four years past which indicates the conditions ordinarily met with as regards river stages at various times of year.

In the balancing of interests between the traffic on the river and that across the bridges, it is believed to be fair and just that for boats of excessive size and height the navigation of the river above a 15-foot stage be eliminated from the problem; (1) because of the comparatively small number of these boats; (2) because of the questionable necessity of having such high boats at all; (3) because of the period of the year when these extreme stages are reached; (4) because these periods of time are so limited in length; (5) because of the generally accompanying swift currents, and (6) because of the oft-times accompanying dangerous floating drift and floating ice.

As to the height of vessels, it is to be noted that the great bulk of navigation under the bridges is not through traffic, but is simply movements about in the lower stretch of the river which forms part of the harbor of Pittsburgh. The commodities moved are nearly all sand, gravel and coal in barges, which loads are almost invariably taken up stream while the downward movement is mostly of empty barges. These barges are mostly moved by harbor tugs. The harbor tugs actually in use are from 22 to 27 feet high, averaging about 24 feet.

The heights of the Monongahela standard towboats vary from 24 to 32 feet, averaging about 28 feet. Out of a list of 28 such boats but 5 exceed 28 feet in height.

The few packet boats running on the river are of moderate height and can be accommodated in the harbor under the bridges at ordinary river stages. The amount of business that could be done by a few packet boats of extreme and unnecessary height is so small that to raise the bridges to a sufficient height to accommodate it would place an entirely unjustifiable tax and inconvenience upon the far greater business interest of the city concerned in crossing the river.

The following tables show the average number of days per annum during which various types of existing vessels would be prevented from navigation by bridges of various assumed heights above the Davis Island Pool:

TABLE SHOWING EFFECT OF VARIOUS CLEARANCE HEIGHTS UNDER BRIDGES

=============================================================================
|Present| | | |Present| | |
Assumed bridge |6th St.| | | |6th St.| | |
height above pool |bridge | 37 | 42 | 47 |bridge | 37 | 42 | 47
level in feet | 33 | | | | 33 | | |
---------------------+-------+------+------+------+-------+------+------+----
|Total number of days per |Total number of days per
Types of Vessels |annum when clearance |annum when clearance would
|would be insufficient. |be insufficient excluding
| |days when river is above
| |15-foot stage.
---------------------+-------+------+------+------+-------+------+------+----
Harbor tugs, average | | | | | | | |
height 24´ | 12 | 3 | 1 | 1 | 3 | 0 | 0 | 0
| | | | | | | |
Harbor tugs, maximum | | | | | | | |
height 27´ | 36 | 9 | 1 | 1 | 28 | 0 | 0 | 0
| | | | | | | |
Monongahela boats, | | | | | | | |
ordinary maximum | 57 | 12 | 2 | 1 | 48 | 3 | 0 | 0
height 28´ | | | | | | | |
| | | | | | | |
Monongahela boats, | | | | | | | |
extreme maximum | 198 | 57 | 9 | 1 | 189 | 48 | 0 | 0
height 32´ | | | | | | | |
---------------------+-------+------+------+------+-------+------+------+----

In drawing conclusions from the above table, as a basis for plans governing the expenditure of millions of dollars in construction and the permanent establishment of conditions of navigation and of traffic over the bridges and the enormous business interests concerned, it is important to bear in mind that the types of vessels here considered are antiquated, and can undoubtedly be materially changed in many particulars to the benefit of all interests.

As bearing directly on this question of boats and bridges, attention is invited to the following extract from the report of Hon. D. S. Alexander, chairman of the River and Harbor Committee of the United States House of Representatives, in submitting for action of the House the last River and Harbor bill on February 11th, 1910:

_Modern Type of Boats for Non-tidal Rivers._--"The British Government has been designing shallow-draft boats for use on the Nile, and the German and Austrian governments have been working along similar lines with reference to methods of transportation on the Rhine, the Danube, the Elbe and other waterways. The boats designed have been very successful, having been used in connection with modern loading and unloading appliances. On our western rivers little change has been made in the design of towboats, barges, etc., since 1860, and it is believed that a design embodying the best points of modern vessels, with modern machinery and cargo handling devices, might lead to a marked increase in the traffic on the non-tidal rivers of the United States, especially after permanently improved channels are available.

"It is believed that the appropriation of $500,000 to be expended in the purchase of plant for use in connection with the work of improvement of the river will also provide for experiments to be carried on by the Government which will result in improving the present type of river freight carriers; and also that these tests can be made in no other way, since the expenditures and uncertainties involved preclude the use of private capital for the purpose. As a result of the tests or experiments it is hoped that a large saving to the country at large may accrue from decreased costs of transportation, and that a type of carrier may be developed which will also reduce the cost of all bridges across navigable streams due to lessened requirements in the matter of head room."

This report of Colonel Alexander, the very able Chairman of the River and Harbor Committee of the House of Representatives, is worthy of serious consideration. Such an investigation and experiments to determine the best type of carriers to use on the river seems certain to be provided for and may result in clearly demonstrating that no necessity exists for raising the Allegheny bridges at all, in accordance with the possibility outlined by the closing paragraph of Colonel Alexander's report above. The appropriation of $500,000 as recommended by Colonel Alexander is included in the River and Harbor bill which has passed the House of Representatives and Senate. There is every probability that it will become a law.

A vast amount of water traffic is carried on inland waterways all over the world under fixed bridges with far less head room than is provided for under the Allegheny River bridges. It is customary in other parts of the country and the world to establish for rivers a minimum head room for bridges at a high navigable stage, which stage is considerably lower than the maximum or even the ordinary high flood stage. For instance, in the new barge canal being built by the State of New York at a cost of $108,000,000 the minimum head room under all stationary bridges is fixed at 15½ feet at the _high navigable_ stage of the water. The high _navigable_ stage is based chiefly upon what is a _safe_ navigable stage, taking everything into consideration. It is by no means a very high stage. As this canal runs through the canalized Mohawk, Oneida, Oswego, Seneca and Clyde rivers, the situation is comparable with that on the Allegheny. The depth of the canal at low water is to be 12 feet, so it is seen that the clear head room is but about 25 per cent greater than the minimum depth of the water. _The boats must be made to fit the bridges, and not the bridges to fit the boats._ It is estimated that the amount of traffic which will pass through these canals about 450 miles long and under these 15½-foot bridges will be about 20,000,000 tons annually, many times the amount making use of the Allegheny River. The present Erie, Champlain and Oswego canals in the State of New York, which have been in operation for about 80 years, are crossed by several hundred bridges giving a clear head room of 13 feet. No complaint about this head room is known to exist, notwithstanding that steam vessels are largely used for navigation purposes on the canals. _The boats have to be made to fit the bridges and not the bridges to fit the boats._

At Paris, the river Seine running through the city carries a very large amount of business. Annually about 20,000,000 passengers, and about 11,000,000 tons of freight are carried on boats of various kinds. There are 36 bridges which span the river and must be passed by the water-borne traffic. The clear head room under these bridges at the highest navigable water varies from 11.25 feet to 21.88 feet. By highest navigable water is meant the stage of water when by reason of floods or currents, navigation ceases. This Paris water-borne freight traffic on the Seine amounts to fully 7 times that of the Allegheny River and passes under 5 times as many bridges, with minimum available head room at high navigable stages just about one half that under the present bridges over the Allegheny at a 15-foot stage. The conditions of navigation on the Seine at Paris are practically the same as those on the Allegheny at Pittsburgh. _In Paris the boats are made to fit the bridges and not the bridges to fit the boats._

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.

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.

As a permanent arrangement of piers for the above three bridges either of two logical plans may be adopted. The first is to retain the existing two-spans center-pier arrangement of the Sixth Street and Seventh Street bridges, conforming to the center pier plan required by the United States Engineers for the new North Side Point bridge, and reconstruct the Ninth Street bridge upon the same general plan. The other is to reconstruct all three bridges with two piers and three spans each, as recommended by the local office of the United States Engineers. The first or central pier plan has the merit of economy of construction in that it involves the construction of no new piers for the Sixth Street and Seventh Street bridges, and permits the continued use of the existing superstructures of the Sixth Street and Seventh Street bridges by simply raising them to the elevation that may be decided upon and ordered. So far as we can ascertain, in view of the center pier plan adopted for the North Side Point bridge, the advantage to navigation appears to lie on the side of adhering to a center pier plan for these bridges also. On the other hand, there is no doubt that three-span bridges could be made more agreeable in appearance than two-span bridges. But the possible gain in appearance alone does not appear sufficient to justify the adoption of three spans.

The next bridge above Ninth Street is that of the Pittsburgh, Fort Wayne and Chicago Railroad. This has been constructed with two main piers providing one main central channel 337.5 feet wide and three other piers giving four channels from 155 to 163 feet wide. Owing to the bend in the river at the bridge and the distance above the Ninth Street bridge, there is no valid objection to this single main central channel at the railroad bridge connecting either with two channels divided by the central piers of the bridges below, or with a central channel if those bridges should be reconstructed on the three-span plan.

The Sixteenth Street bridge has been constructed with 3 piers dividing the river into 4 channels of about 150 feet each; the clear head room beneath it is less than that now given by the bridges below it. The best arrangement to be made with this bridge is to require it to be rebuilt without the central pier, leaving a central channel about 320 feet in width between the two side piers to correspond with the railroad bridge just below it. It is an old, covered, wooden bridge, in poor physical condition, and, as previously noted, it is probable that it must be raised anyhow in connection with eliminating railroad grade crossings on the approaches.

The Thirtieth Street bridge has its piers properly spaced to leave a central channel 285 feet in clear width and no changes are required in pier and channel location at this bridge.

The Thirty-third Street or Pittsburgh Junction Railroad bridge of the Baltimore and Ohio System has 3 piers, giving a main central channel of 232 feet wide, with side channels 195 feet wide, and on the Herrs Island side of 150 feet. No change is needed in the location of the piers and channels at this bridge.

The Forty-third Street bridge is built with 3 piers, making 4 channels each of about 160 feet wide. It gives less clear head room at high river stages than most of the lower river bridges. It is an old wooden bridge, in poor physical condition. The best arrangement for this bridge is to treat it as the Sixteenth Street bridge, and to require it to be rebuilt, omitting the central pier and leaving a central channel about 300 feet wide, to correspond with the bridges below it. The elimination of railroad grade crossings on the approaches to this bridge is already a pressing public need and must soon result in its raising or reconstruction at a higher level.

_Considerations against Requiring Changes in Bridges To Be Made at Present._--The following important questions, having a direct bearing upon the proper design of permanent bridges across the Allegheny River, are now under consideration:

1. The Flood Commission is getting data for studying the question of a protective embankment along the river front, and of the proper grades of streets and bridge approaches in the region subject to inundation. The design of such flood-protection works should have important bearing upon the grade, location and design of the permanent bridge abutments. This Commission is also studying the question of impounding the flood waters of the Allegheny and Monongahela Rivers in their upper valleys, which may result in materially lessening the height and velocity of floods in the harbor of Pittsburgh, and consequently, simplify the bridge and navigation problems of the harbor.

2. The question of the best routes for surface cars and rapid transit lines crossing the Allegheny River is now being studied for the City as a part of a comprehensive plan for traction improvements. The result of these studies might readily affect the design of the new bridges.

3. The government experiments recommended by Colonel Alexander of the River and Harbor Committee and authorized in the River and Harbor bill just passed by Congress and providing for the development of a more economical and efficient type of river-boats, requiring less head room than the present antiquated types, may soon show results that would have a decided influence in determining the reasonable clearance heights of bridges.

4. Attention is also invited to the fact that the people of Pittsburgh have voted to expend about $7,000,000 in certain public improvements. Among these are the cutting down of the "Hump," an obstructive hill in the city's midst, widening some streets and filling certain other streets in the North Side and West End that are flooded at high river stages. The material from the "Hump" in the vicinity of the Court House is to be hauled to these North Side streets across the lower Allegheny bridges under question. The work is of great magnitude and it will take at least two years to complete it. Any material alteration to the bridges such as proposed by the Board of Engineers will require a long time to be carried into effect. While this bridge work would be under way, the transportation of the material excavated from the "Hump" and the filling up of the low grade streets of the North Side would have to cease or would be carried on with great difficulty and inconvenience to other traffic. This would tie up the whole work while it is in progress, causing material injury to the city, for it is to be extremely annoying and bothersome while it is in progress, and the longer this period is strung out the worse it will be.

For all of the above reasons we believe that to precipitate the actual reconstruction of the bridges at this time would be most undesirable for the city and prejudicial to the best results, in the long run, for all concerned.

RECOMMENDATIONS

In conclusion we beg to recommend as follows: 1. That the Sixteenth Street and Forty-third Street bridges, which are obstructions to navigation on account of their pier locations, narrow channels, and exceptionally low clearance height, be required to be rebuilt with their piers so located as to give channels conforming to the neighboring bridges, and that their elevation be fixed with regard to eliminating the railroad grade crossings on their approaches, but the minimum clearance shall be fixed in accordance with the closing paragraph below.

2. That the Ninth Street bridge should be rebuilt as soon as practicable with a center pier and two wide spans conforming to those of the Sixth Street and Seventh Street bridges. The design of the new Ninth Street bridge, however, should not be finally determined and erection begun until a definite plan for comprehensive improvements in the traction system between the two sides of the river has been decided upon. Unless new circumstances develop before the construction of this bridge is begun that materially affect the problem of clearance height, the elevation should be fixed in accordance with the closing paragraph below.

3. That all questions pertaining to changing the elevation of the Sixth Street, Seventh Street, Fort Wayne, Thirtieth Street and Junction Railroad bridges be deferred to await the report of the Pittsburgh Flood Commission and the resultant action; to await the report on a comprehensive plan for traction improvements; to await the completion of the work projected by the City in cutting down some streets and filling others; and to await the results of investigation of river-boat design and construction provided for in the River and Harbor bill just passed by Congress.

4. That, if it is deemed essential and necessary at present to decide upon the elevation to which all Allegheny River bridges must be made to conform, this elevation be fixed so that there shall be a clear head room of substantially 37 feet above pool level, varied so as to give at each bridge a clear head room of 28 feet when the river is at a 15-foot flood stage. This height to be maintained over the entire main span where there is a central span and for 180 feet on each side of the central pier where there is a central pier.

We have the honor to be, very respectfully,

Your obedient servants,

THOMAS W. SYMONS,
Col. Corps Engineers U. S. A., retired,

FREDERICK LAW OLMSTED.