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ELECTRIC RAILWAY JOURNAL · Vol. 73, No. 5 · February 2, 1929 · pp 203-206.
Concreted Track for New York City Subway
By Robert H. Jacobs, Division Engineer, Board of Transportation, New York City
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| Type II roadbed on tangents and curves of 2,300-ft. radius and over. |
Extensive study led to the adoption on the new subway of wooden blocks set in concrete for the rail support except under special work. In this article the author outlines the numerous advantages of this type of construction.
While the fundamentals of all track construction are largely the same, from the pioneer work in the West to the present-day subways. tracks for rapid transit subway operation involve several aspects that are not entirely paralleled by steam railroad. Subway tracks are installed over a rigid floor instead of on a yielding subgrade and are not affected by frost and other climatic conditions, as is the case of open track on steam railroads. While provisions for drainage must be made, they are of an entirely different character from those usually required for other railroads. Likewise, the smaller temperature range in subways requires providing for less expansion in the rails. and motor-driven cars react upon the tracks quite differently, from the driving wheels of steam locomotives. The fundamental requirements for subway tracks are in many ways quite similar to those for street railways, although there are obviously many points of difference both as to traffic and physical conditions to be met.
The rapid transit railroad system of Greater New York now under operation by the Interborough Rapid Transit Company and Brooklyn-Manhattan Transit Corporation consists of 216 miles of structure (subway and elevated) and 631 miles of track, exclusive of yards. The new independent city subway system was started in 1925 and, as at present laid out, consists of about 55 miles of structure and in the neighborhood of 175 miles of running track, exclusive of yards.
The contract drawings for the construction of the original subway (now operated by the Interborough Rapid Transit Company and known as Contract 1) indicated that in the underground portions of the railroad the track should consist of rails laid on a continuous bearing of wooden blocks, the blocks to be held in place by steel channels secured to metal crossties imbedded in concrete. This contemplated type of rigid construction required less depth below the base of rail than for ballasted track, and the subway structures were built accordingly. Although no such type of track had been used for high-speed railroads, a short stretch of it was installed and tested out under traffic on the Long Island Railroad. When the time came for laying the tracks in the subway the conservative attitude of the operating company toward the adoption of this new type of track resulted in the final adoption of the ballasted type of track in place of that originally contemplated. This necessitated raising the base of rail to provide for ballast, thereby reducing the overhead car clearance. At the same time it permitted only a very shallow track construction with but 5-in. ties and 5 in. of ballast beneath the ties. On later work 6-in. ties with a 7-1/2 in. layer of ballast were adopted as the standard construction.
The tracks for the original subway and elevated railways (Contracts No. 1 and No. 2) were installed with 100-lb. modified A.S.C.E. rail, using ribbed tie plates pressed into the ties. The tracks for the elevated extension of the original subways were constructed somewhat similar to the existing Manhattan Elevated Railroad lines, except that 100-lb. modified A.S.C.E. rail was used instead of the 90-lb. special section in use on the Manhattan Elevated lines.
Prior to the preparation of track standards for the additional lines for the present operated dual system, conferences were held between representatives of the city and both operating companies. This resulted in the adoption of uniform standards except for certain items on which the two companies did not agree, the most important of which were the types of switches and the sizes of ties and guard timber for elevated railroads. Separate standards were therefore adopted where affected by these items for track to be operated by each of the companies. Housed switch points were adopted for Brooklyn-Manhattan Transit Corporation lines, and lapped switches for Interborough Rapid Transit Company lines ; 6x8-in. ties and 6x6-in. outside guard timber were adopted for Brooklyn-Manhattan Transit elevated lines and 8x8-in. ties and 6x8-in. outside guard timber were adopted for Interborough Rapid Transit elevated lines.
After the completion of the original rapid transit system (Contracts No. 1 and No. 2) and prior to the installation of the tracks for the dual system, an interesting type of track construction had been adopted and installed in the Detroit River tunnels and in the Grand Central Terminal of the New York Central Railroad, as well as in the Pennsylvania Terminal and in a portion of the tracks of the Pennsylvania Railroad between the terminal and Long Island City, and also for portions of the Hudson-Manhattan Railroad. This special type of track, while differing somewhat in detail in the various localities, consisted essentially of short wood blocks imbedded in concrete for the support of the rails, with a trough between the rails. This type of construction was adopted by the city and installed at the stations of the dual system as well as in the Montague Street, Fourteenth Street and 60th Street river tunnels, where it proved so satisfactory that its use has been greatly extended for the new city subway system.
Track Standards for New Subway. For the new city subway it is planned to install concreted track throughout, except that ballasted track will be used for special work and for short stretches of track between special work, also for lay-up tracks and for tracks in yards.
The ballasted track, known as type I, is laid in a concrete trough, provided under the subway construction contracts for a planned depth of 7-1/2 in., for ballast under the ties. Eighteen 6x8-in. ties to the 33-ft. rail and 7-1/2x9-in. shoulder tie plates with cut spikes are standard construction. A view is given of a section of such track.
The concreted type of track, known as type II, is installed in a concrete trough identical with that provided for the ballasted track. The rail is laid on separate 6x10-in. creosoted wood blocks, spaced eighteen to the 33-ft. rail, imbedded in concrete to approximately the tops of the blocks, and sloping toward the center of the track for drainage. This construction provides a trough between the blocks and extending below the level of the bottom of the blocks. Screw spikes instead of cut spikes are used throughout. Tie plates are used with bosses to support the heads of the screw spikes so as to provide a space of 1/16 in. between the flange of the rail and the underside of the head of the screw spike, as will be explained in more detail later.
In extending the use of concreted track it was realized that we were entering upon a program of the most extensive use of rigid track construction undertaken anywhere in this country. This decision was made after a careful study of the tracks of this character, which had been in operation for the last twelve years. During this period these tracks required practically no maintenance except rail renewals and the tightening up of track bolts. There is every reason to expect that this condition will continue for a great many years or until it is necessary to renew the ties.
Six Marked Advantages of Concreted Tracks. The advantages of concreted track are:
1. More satisfactory drainage. In our ballasted track, drainage is through the ballast into drain boxes connecting with a drainage system below the subway floor. With the concreted type of track, the greater part of the drainage is carried in the track trough, and it is only necessary to provide under drains in special cases where it is expected that the flow will be such as to make it undesirable to carry it all in the track trough, as well as in certain localities where the grades are very flat. When ballast is used, it soon becomes clogged and is therefore unsatisfactory for drainage purposes.
2. Better riding qualities. Due to the permanency of alignment and grade, continuous good riding qualities of the track are assured with resulting favorable effect upon the rolling stock.
3. Better maintenance conditions. In the case of subway tracks, the depth of ballast is necessarily limited, due to the large expense of increasing the depth of the subway, the standard depth being but 7-1/2 in. under the ties, whereas in ordinary railroad construction, with ballast placed on an earth subgrade, the depth of ballast varies from 12 in. to 24 in. The frequency of train movements in subways and the constant tamping of ballast required to keep the track in surface and line causes a certain amount of stone dust, which, if allowed to accumulate, eventually blocks the drainage. This necessitates frequent renewals of stone ballast under very difficult conditions. The Interborough replaces ballast between stations about every ten or twelve years, and through the stations more frequently. This maintenance work has to be done during a few hours at night with large gangs of men and with materials handled directly from work trains. All of this work is dispensed with in the case of concrete track. In many places there will be little or no flow of water, and the track trough of the concrete track provides a very convenient space for the, storing of rail for renewals.
4. Better sanitation. Concreted track provides a surface that can easily be kept clean, whereas the filth and debris which accumulates in the ballasted track can be removed only by taking out the ballast.
5. Safety. From the point of view of safety this type of track has distinct advantages. The newspapers from time to time report that passengers fall off the platforms and are killed by passing trains. In several instances where such accidents occurred at places where concreted track is used, persons have rolled into the track trough and the trains passed over them without seriously injuring them. In the case of ballasted track, the distance from the under side of the cars to the top of the ties is so small that it does not allow a train to pass over a person.
With the concreted track it is possible to reduce to a minimum the number of workmen required to maintain the surface of the track. As a large number of men are required on the maintenance of ballasted track under operation, it is expected that the adoption of the concreted track will result in reducing very considerably the number of accidents to operating employees.
6. Economy. Concreted track, in providing for drainage in the trough between the rails, makes it possible to effect a large saving due to the omission of under drains, which with their manholes and connections require excavation, in earth or rock, below the subgrade of the structure at considerable cost. Taking this into account, the cost of concreted track has been estimated as being slightly less than for ballasted track. The labor cost of maintenance, however, is very much less for the concreted track according to our estimates, based upon the very conservative assumption that the wood blocks will not have to be renewed for 36 years. This makes concreted track much more economical than ballasted track.
Although it is believed that train resistance is considerably less on rigid concrete track than on ballasted track, no tests under rapid transit conditions have been made to substantiate this belief. A somewhat limited test on the Pere Marquette Railway under steam road conditions over about 1,200 ft. of concreted track indicates a reduction of about 15 per cent in train resistance.
With the concreted track brought to proper alignment and grade, the wear and tear on the cars should be considerably less than is the case with ballasted track, which, even under the best conditions practicable, is more or less out of surface.
The adoption of separate wood blocks for the support of the rails was, of course, a radical departure from the standard railroad practice of supporting the two lines of rails on the same tie in order to assure the maintaining of the gage. This situation, however, is entirely taken care of by the backing up of the ties with concrete. On the earlier construction, 1-in. anchor bolts were placed at both ends of every tie block. These anchor bolts extended down into the concrete bed of the track construction. It has been shown from observation of the tracks over a period of twelve years under operation that these anchor bolts serve no useful purpose, with the possible exception of helping to anchor the ties supporting the guarded rail on sharp curves. In our present work anchor bolts are omitted except for the low side of guarded curves where they are provided to obviate the possibility of tight gage due to the pressure of the wheel flanges against the guard rail.
Although it appears that the time for the renewal of the
ties is far distant, we have given this matter serious
consideration. There is no question but that it will involve a large
amount of work. In a few cases where reconstruction of this track has
been necessary the blocks have been removed and replaced under traffic
without serious difficulty and with satisfactory results. We have also
constructed a considerable amount of concreted track under
operation. In the event of general renewal it is expected that
somewhat smaller ties will be used that can be placed in the grooves
left in the concrete and secured in positions with grout or some
asphaltic compound.
In general, regardless of ties and roadbed, there are
several types of standard construction based on curvature. They may be
designated as follows:
1. Tangent track and curves of more than 3,000-ft.
radius. This track is installed in accordance with general practice,
with 4-ft. 8-1/2-in. gage and single spiked—- that is, with one spike
on each side of each rail.
2. Curves of from 3,000-ft. to 2,300-ft. radius. The
only material difference in this type of construction from the above
mentioned type is that an additional spike is installed on the inside
of both rails.
3. Curves of 2,300-ft. to 1,000-ft. radius. Guard rails
are installed adjacent to the gage side of low rail on all curves of
less than 2,300-ft. radius, including transitions. The inside of the
unguarded or outside rail is double spiked, while the running rail and
guard rail on the inside of curves are single spiked. No rail braces
are used on curves in this classification.
4. Curves of 1,000-ft. to 500-ft. radius. Rail braces
are placed on the outside of the rails on the high side at every other
tie on all curves of less than 1,000-ft. radius, and on the inside of
guard rails at every third tie on all curves from 1,000-ft. radius to
500-ft. radius. The rail braces are spiked through the tie plates with
three 1x5-1/2-in. screw spikes. On this type of construction we are
providing extra tie blocks for the support of an additional rail
toward the center of the track. The rail renewals on sharp curves are
rather frequent and it has been found advantageous at the time of the
first rail renewal to place the old rail inside of the guard rail.
This rail is then bonded instead of the new rail, rendering it
possible to make all future rail renewals without disturbing the
bonds. This additional rail may have some advantage as an extra
safeguard in case of derailment.
5. Curves of 500-ft. radius and under. This type of
curve construction differs from that for 1,000-ft. to 500-ft. radius
in that instead of installing rail braces on the guard rail at every
third tie, they are installed at every other tie, and four
7-ft. 5-in. crossties to every 33-ft. rail length are substituted for
an equivalent number of short blocks.
Sources: Electric Railway Journal, McGraw Hill Company, Digitized by Microsoft, Americana Collection, archive.org.
Route of the New York City subway now under construction. Ballasted track, known as type I, is used only for special work, for short stretches between special work, for lay-up tracks and in yards. 
Concreted track, known as type II, is used generally throughout the subway. On curves of 500-ft. radius or less, four 7-ft. 5-in. cross ties to every 33 ft. of rail are substituted for an equivalent number of blocks. Tangent track on vertical curve.
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