Design of the Diagonal Station and Connection (1918)
Public Service Record · Vol. V, No. 12, December 1918.
Design of the Diagonal Station and Connection.
By Olof A. Nilsson, Designer, Division of Designs
One of the most important of transportation centers of New York, when the rapid transit systems now being built are completed, will be what has become known as the Diagonal Station, located diagonally across and beneath 42nd Street between Park and Lexington Avenues, and extending approximately from the intersection of Park Avenue and 41st Street to Lexington Avenue and 43d Street.
North of 42nd Street, facing Park Avenue, the New York terminus of the New York Central and the New York, New Haven and Hartford railroad systems, namely the Grand Central Terminal. On 42nd Street just west of Park Avenue is located what was the Grand Central Station of the First Subway, the route of the latter turning from Park Avenue at this point and extending west under 42nd Street to Times Square, thence continuing via Broadway and other thoroughfares through the northerly end of Manhattan and on to Van Cortlandt Park by the Broadway branch and into The Bronx by the Bronx Park branch. Two blocks east runs the Third Avenue elevated railroad with a shuttle service to and from the Grand Central Terminal. As to surface lines, there are the cross-town line on 42nd Street, the Lexington Avenue line to the east, and the Park Avenue-Madison Avenue line which, in Park Avenue south of 41st Street, runs underground in a tunnel above the level of the subway tubes.
General plan of diagonal station at 42nd Street and Grand Central Station. (Click to enlarge.)
Subway History. When, in 1913, the Dual System Contracts were adopted, these were included in the portion of the system assigned to the Interborough for operation, among other lines, the Lexington Avenue subway, which was a part of the previously planned Triborough route, and the Queensborough subway, which, originally known as the Steinway tunnel, had been begun as early as 1892, and was built as two single-track tunnels from Long Island City under the East River and 42nd Street, ending in a loop under Park Avenue in front of the Grand Central Terminal.
The Lexington Avenue line, branching north of the Harlem River in a westerly line on Jerome Avenue leading to Woodlawn and an easterly one extending to Pelham Bay Park, was, under the terms of the contract, to connect with the original subway south of 42nd Street, thus to form the easterly of the two north and south four-track main lines of the Interborough system in Manhattan. The Queensborough subway was to be extended west to Times Square and the Long Island City end, after being extended to Queensborough Plaza, was laid out with two branches, the Astoria line running north and the Woodside and Corona line running east. With the completed system in operation, the portion of the original subway in 42nd Street was abandoned for through traffic. Two of its tracks were assigned for shuttle trains between the Times Square station on the west and the Diagonal station on the east main line. The two remaining tracks may be used for the extension of the Queensborough subway.
It is the intention further that the uptown tunnels of the Hudson and Manhattan Railroad, connecting New York with Jersey City, Newark and other New Jersey communities, shall, in the future, be extended to this point from the present terminal at 34th Street and Sixth Avenue.
Plate 2 shows these various rapid transit lines meeting and intersecting around 42nd Street and Park Avenue (the surface lines being omitted in order to avoid confusion).
Problem at Focal Point. The problem to be solved at this focal point of present and future transit lines was twofold:
First: To effect a physical connection between the old subway in Park Avenue and the new one in Lexington Avenue without interruption and danger to subway traffic during the period of construction and in such a manner that at the end of this period the traffic could be diverted without serious interruption.
Second: To locate and design a subway station which would adequately serve the anticipated traffic. The proximity of the Grand Central Terminal, a large proportion of whose incoming passengers will continue their journey by the subway, the intersection of two subway lines, and the shuttle service to a third one are conditions producing a large transfer traffic, which, plus the traffic originating in this rapidly developing neighborhood, tend to make the Diagonal station in point of number of passengers passing through it one of the largest in New York. It was, therefore, important to make the station large enough to accommodate this enormous passenger flow and to locate it so that the annoyances incident to effecting a transfer would be reduced to a minimum.
Final Solution. The solution was accomplished by making the Park Avenue-Lexington Avenue connection diagonally across 42nd Street and utilizing this diagonal connection for a large express station. This location brings the station as close as possible to the Grand Central Terminal and permits intercommunication of passengers by means of comparatively short underground passages. It also gives a convenient shuttle connection as well as another with the Queensborough subway, the latter by placing the Queensborough station directly below the Diagonal station. This is shown on Plate 1, which gives a general outline of the station, the adjacent Grand Central Terminal, the shuttle station and the Queensborough station below, indicating also the connection to the old Park Avenue subway.
The latter is, north of 34th Street, built as two double-track arch tunnels, 68 feet center to center, merging as they approach 42nd Street into one structure built of steel bents and concrete. The grade north is a rising one of about 1.15%. The Diagonal station is placed at such an elevation that at the westerly end the two express tracks in the middle, by a maximum downgrade of 3.5%, are carried under the old easterly (northbound) tunnel. Turning south the new express tunnel continues between the two old tunnels on a rising grade until, at the proper level, it divides and breaks right and left into the latter, and a junction is effected between the new and the old express tracks. In the same manner the new southbound local track is carried under both the old tunnels and runs south on the westerly side of the old line, connecting with the old southbound local track near 38th Street. The new northbound local track, connecting to the old track between 40th and 41st Streets, has a downward grade as it runs north and turns into the Diagonal station, so that by the time the platform ends are reached all four tracks are at nearly the same level.
Solution at Junction Point. The design providing for the difficult work of joining the old and the new tunnels in Park Avenue is indicated in plan and section in Plates 3 and 4. As shown in the cross-section, the structure was enlarged by removing one-half of the old masonry arch and excavating the rock to the required width. The crown thrust of the half arch left undisturbed is transmitted through the new roof construction into the rock on the opposite side, and the vertical load is taken up by a line of columns in the center of the old tunnel between the tracks.
Plate IV. Section of connection of old and new work.
North of the portion described above, where the new track is entirely outside the old tunnel, the new tunnel is built first in a rectangular shape with steel roof beams and columns and further north as a twin arch tunnel with a line of steel columns in the center.
Plates 5 and 6 show in plan the reconstruction of the old northbound tunnel for a length of about 200 feet from the point where the new northbound local track begins to deflect east to the point where steel bent construction was used originally. 0n this portion of the work the street was excavated until the old arch was uncovered. The arch was then removed and replaced by a structure of steel bents and concrete. This structure is carried over the new express tunnel on plate girders spanning this latter and in turn supported by columns which are carried to the new subgrade below.
Plates V-VI. Upper: Plan at roof level of old tunnel as reconstructed. Lower: Plan at roof level of new express tunnel. (Click image to enlarge.)
Plate 7 is a cross-section just south of 41st Street, which shows all the tunnels old and new, in Park Avenue at this point including the reconstructed old northbound tunnel described above and shown in plan on Plates 5 and 6.
Plate VII. Cross-section at point on Park Avenue south of 42nd Street indicated by line B-B on plan. (Click image to enlarge.)
Design of Station. The Diagonal station proper, as indicated on Plate 1, is of the ordinary type for four-track express stations with twin island platforms, 480 feet long, one serving northbound and one southbound traffic. Each platform has eight stairways, six leading up and two down. The latter connect to a ramp and passageway 12 feet wide by which passengers may transfer to and from the Queensborough subway, directly below. The former, 10 feet wide, lead up to two mezzanine floors above. The larger of these mezzanines, extending under the full width of 42nd Street and under part of the old Grand Union Hotel plot, covers about 25,000 square feet. Its floor surface at elevation 128.4 feet is about 17 feet below the street level at the principal entrances, which are located on 42nd Street, one on the southerly and two on the northerly side of the street. A fourth entrance is located in Park Avenue between 41st and 42nd Streets.
In addition to these direct street entrances, this mezzanine is connected by means of underground ramps and passages to incoming and outgoing trains of the Grand Central Terminal, to several important buildings in the neighborhood and to other street entrances on Lexington Avenue, on 45th Street and in 42nd Street west of Vanderbilt Avenue. A ramp at the westerly side leads to an island platform serving the shuttle trains to Times Square. Finally, communication with the Queensborough Subway station below is provided by three elevators and one emergency stairway.
The smaller mezzanine near the easterly or northerly end of the station is entirely within the limits of the Hotel Commodore and is about 44 feet wide and 90 feet long. It has two entrances, both connected to the ground floor of the hotel. The one will principally serve the hotel guests and railroad passengers, the other will take care of street traffic east of and on Lexington Avenue. The latter has two openings to the street, one on 42nd Street and the other through a passageway under the sidewalk on Lexington Avenue north of 43rd Street.
Entrances through Buildings. Worthy of note is the fact that all entrances built for this station are through adjacent buildings. As the density of sidewalk traffic increases, a subway entrance becomes either an increasingly serious obstruction, if placed on the sidewalk, or, if placed through an adjacent building leaving the sidewalk free, an asset of increasing value to the owners of the building.
Except for the portion directly under 42nd Street the Diagonal station is located almost entirely under private property. It was, therefore, necessary to build a subway structure capable of sustaining such loads as might be imposed by future buildings and also to see that in the design no avoidable detrimental restrictions were imposed on the architects of these future buildings. Owing to different conditions this problem was solved differently for the two properties involved.
On the property north of 42nd Street, belonging to the New York Central Railroad Company, it had already been decided to erect a large hotel, the Commodore, and plans for this hotel were carried on ahead of or simultaneously with those for the subway structure. The subway columns were located by the usual requirements for station bents, 15 feet center to center, two column lines in the platform and one between the express tracks. They were carried up through the subway roof. The building columns rest on an irregular and somewhat elaborate system of girders, which transmits the building loads into the subway columns. The main roof of the subway forms the basement floor of the hotel; between the basement ceiling and the ground floor of the hotel there is a space of about 8 or 10 feet which is utilized for this girder system.
The Grand Union Site. The use to which the plot south of 42nd Street, originally occupied by the old Grand Union Hotel, was to be put was unknown and it was thus not possible to provide for any definite type of building. Efforts on the part of the Commission for a voluntary agreement on reasonable terms with the original owners having failed, the plot was acquired by the City under condemnation proceedings with the end in view of reselling, subject to an easement, when construction was completed and the market was favorable.
It was, therefore, necessary to assume the maximum height and weight of a building that could and in all likelihood would be erected on the plot, and provide for the loads of this imaginary building. Two methods were possible: One to design the subway roof for a uniform load per square foot, not less than the average weight per square foot of the assumed building, the loads from the building columns then to be distributed over the subway roof by means of grillages; the other to decide on an economical and advantageous panel division for such a building as might be anticipated for this plot and to design the subway roof for building loads at the points thus obtained. Any disadvantage that might be inherent in this second method, in thus restricting the panel spacing of the building was considered to be more than offset by the cheaper construction it offered and by the saving of valuable basement space which under the first mentioned method would have to be taken up by the grillages.
The plot was, therefore, divided up into a number of equal spaces in both directions, resulting in a column spacing of 20 feet 7 inches in one direction and 21 feet 6 inches in the other. It so happened that the diagonal lines drawn through the column centers thus obtained were almost normal to the longitudinal axis of the station and the distances between these diagonals were also nearly equal to the standard column spacing of 15 feet for stations.
Assume 25-Story Building. Taking advantage of this fact, the bents were located on the diagonal lines connecting the columns, thus centering every column on a bent and escaping the necessity of a double system of girders for the transmitting of building loads from base of building column to subway columns. A 25-story building was assumed to be the highest likely to be erected on this plot. Live and dead loads from such a building were computed on the basis of the New York building code as in force in 1915, and used in designing the subway bents.
Plate 8 shows a typical bent. The girders supporting the building columns are double and of varying depth, according to the magnitude of the moments and shears. A cast steel slab on the top flange of the girders will serve as a base for the future building columns. Similar slabs are used as caps and bases of the subway columns, and between different tiers of grillage beams.
Plate VIII. Typical cross section at Grand Union Hotel site. (Click image to enlarge.)
As has been shown in the general description of the Diagonal station, the interchange of passengers between the Park Avenue-Lexington Avenue lines and the Queensborough subway was one of the important elements considered in its design and location. As mentioned in the beginning of this article, the Queensborough subway consisted originally of two single-track tubes ending in a loop under Park Avenue. Its reconstruction at this point in order to make it fit into the Dual System is shown in Plate 9.
Plate IX. Cross-section of Queensborough subway at Grand Central station. (Click image to enlarge.)
Tunnel Replaces Tubes. The two original tubes have been replaced for a length of about 475 feet by a large tunnel, increasing in width of span from 41.5 feet at the easterly end to 55.1 feet at the westerly end. This reconstructed portion directly below the Diagonal station forms the main part of the Grand Central Station of the Queensborough subway. It is an island platform station 640 feet long. At the westerly end of the platform are placed the three elevators which as previously mentioned run to the mezzanine floor of the Diagonal station. At about the middle of the platform are two stairways which lead to the ramp by which the platforms of the Diagonal station are reached. At the easterly end of the station an escalator carries passengers to the street.
In general passengers transferring between the Queensborough subway and the Lexington Avenue-Park Avenue lines use the ramps, the elevators being utilized by people going to the street, the Grand Central Terminal, or to the shuttle trains. When the Queensborough subway has been extended to Times Square there should be no occasion for transfer to the shuttle trains at this point by passengers from the Queensborough subway and Queens lines.
The reader will understand that, if the problems confronting the designers of the subway sections described in this article were unusual and difficult, this was no less the case in the carrying out, under most adverse conditions, of the actual construction. While the old structure was being reconstructed, and the masonry removed little by little and replaced by new steel and concrete, the subway traffic in these tunnels went on uninterruptedly day and night, 1500 trains carrying in round numbers 1,000,000 passengers every 24 hours past this point. Very little more inconvenience was caused to the busy street traffic on the surface, and the passengers in the surface railroad tunnel above the subway were as little conscious as were the subway passengers that under and around them rock was being blasted away and the network of tunnels completely transformed. The men on whom rested the responsibility of carrying out this work may well feel gratified that their task is finished and that there has been no serious accident during the three years of building.
The construction has been described in an article by Mr. G. Perrine, published in the Proceedings of the American Society of Civil Engineers, for November, 1917, with discussions in subsequent numbers of the Proceedings by Messrs. Robert Ridgway, John H. Myers, Henry H. Quimby and others. Brief illustrated articles, dealing with special phases of this work, have been published in the Engineering Record of August 28, 1915, and July 22, 1916, and in the Scientific American of July 17, 1915.