Concreted Track--Track Materials Specially Designed... (1929)
Concreted Track for New York City Subway
Electric Railway Journal · Vol. 73, No. 5 · February 2, 1929 · pp 203-206.
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.
By Robert H. Jacobs, Division Engineer, Board of Transportation, New York City.
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.
<i.Long Life of Wood Blocks Expected.</i> It has been realized from the first that every reasonable effort should be made to defer as long as possible the renewal of the wood blocks in the type II track. We have, therefore, endeavored to obtain blocks of the best lumber and creosoted them for longer life. By having most of the holes in the ties drilled before creosoting and by providing spikes of practically exact dimensions, we have minimized the effect of spike-killing. In addition, we have provided ties 10 in. wide instead of the usual 8 in., which makes it possible to plug spike-killed holes, shift the tie plates and drill new holes in the ties. We have found that to date with our 7-1/2x9-in. tie plates, there has been very little tie plate cutting.
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.
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.
Track Materials Specially Designed for New York City Subways
Electric Railway Journal · Vol. 73, No. 8 · February 23, 1929 · pp 325-328.
High carbon rails are used on tangent track, with manganese rail for parts of special work. Most convenient length for handling found to be 33 ft. Accurate manufacture of screw spikes essential. A 150-lb. section is used for third rail.
By Robert H. Jacobs, Division Engineer, Board of Transportation, New York.
Due to the large number of sharp curves on the lines of the new city-built subways in New York, it has been necessary to provide a large amount of guarded construction. This condition has made it necessary for us to provide many special parts to meet the unusual requirements encountered in this situation. The solution of the problems presented has many points of interest. When the track standards for the existing dual system of subways operated in New York by the I.R.T. and the B.M.T. were determined upon, the 100-lb. section had already been adopted for the existing subway. At that time the A.R.A.-B rail section was becoming very popular, and while the Interborough was inclined to favor the extension of the use of the modified A.S.C.E. section for the new lines, the representatives of the city and the B.M.T. favored the new section. After considerable discussion the latter was adopted. The outstanding differences between the two sections are less slope of the head and a narrower and thicker base for the A.R.A.-B rail. While a somewhat lighter rail would, of course, carry the traffic satisfactorily, the use of a larger section is amply justified by the saving in maintenance and renewals.
On account of special conditions, a higher carbon rail than ordinarily used on steam railroads has been found to be practicable. Our specifications call for a carbon content of 0.73 per cent to 0.86 per cent, instead of 0.62 to 0.77 per cent commonly used on steam railroads for this weight of rail. These harder rails, of course, give us longer service.
In general, rolled manganese rail was used on tracks for the dual system on curves of 700 ft. radius and under. The initial purchase of manganese rail for the greater part of the tracks of the dual system was made at a price of about $85 a ton. Since that time the rail was practically doubled in price, whereas the increase in price of the open-hearth rail has been only about 43 per cent. Records of the service on our lines of manganese rail and of high carbon open-hearth rail are not very consistent. Without any question the manganese rail has a much longer life under traffic than open-hearth rail, but it is liable to corrugation. It also has a considerable disadvantage due to the impracticability of cutting and drilling this rail in the field. This affects both original installation and renewals, as well as bonding. On account of these considerations, including its high price, there is a tendency to limit its use. Our standards for the new city subways do not call for the use of manganese rail except for parts of special work most subject to wear.
We are continuing the use of 33-ft. rails, although longer rails are now being used by many railroads. While a reduction in the number of joints is desirable, our determination was based on the difficulties of handling rails longer than 33 ft. in the restricted space in the subway.
The joint bars adopted for the new city subways are similar to those now in use by the operating companies. The "head free" feature providing contact at the top of this bar with the web, instead of supporting the head of the rail near its outer edge, is interesting. Two advantages claimed for this bar are, first, that the joint assumes its final position when applied, assuring the maintenance of perfect alignment through the joint from the time of first application, and second, that the so-called "anvil action" of the wheels on the joints is eliminated, because the underside of the railhead is left entirely free, permitting the railhead to act at the joints the same as throughout other parts of the rail. Another advantage claimed for this "head free" feature is that metal may be omitted from the under faces of the railhead, where it is of no use, and an equivalent amount of metal added to the top of the head, thereby increasing the life of the rail.
The standard "E" bar with alternate round and oval holes is used for all joints except those on the low side of guarded curves and in special work. On guarded curves a so-called "G" bar is used between the running rail and the guard rail. This bar is identical with the standard "E" bar, except that the lower flange is omitted, due to the limited space in which it is to be placed. These bars have round holes only. Bars of standard section are provided with oval holes only for use on the outside of the guard rail, and of the running rail on the low side of curves. The use of bars with all round holes or all oval holes on the low side of guarded curves is due to the necessity of placing the track bolts with their heads on the outside of the rails to facilitate removal.
Welding of rails as an alternative to the use of splice bars has received some consideration, but has not been adopted, largely due to the difficulties of making renewals under traffic.
Contrary to the usual railroad practice, a special type of bolt was adopted for the tracks of the dual system. This bolt has a round neck and a large head, the latter being flattened on two sides so as to fit under a rib at the top of the splice bar in order to prevent turning. This made it possible in the dual system to use splice bars with round holes only. On tangent track and unguarded curves the bolts are placed with the heads on alternate sides of the rail, in accordance with the general practice. As previously stated, on guarded curves it is necessary, in order to be able to back out the bolts, to place all the nuts between the guard rail and the running rail. It was found, after years of use, that this type of bolt, in spite of its advantages, had disadvantages which have led us to abandon it and adopt an oval-neck track bolt with a ratchet or Harvey Grip thread, notwithstanding the fact that it has required the furnishing of bars with special punching for use in guarded construction.
Tie plates for ballasted track are designed for use with cut spikes. The standard "A" plates for use on tangent track and unguarded rails on curves present no special features, but correspond to those in general use. However, special plates are required for use at joints, in guarded construction and in special work. A careful study of manufacturing tolerances was required in order to determine the proper dimensions of the special plates. Tie plates for concreted track are designed for use with screw spikes and require bosses for the support of the screw spike heads in a position to allow a 1/14-in. space between the bottom of the head and the flange of the rail. It was the early practice on some other railroads to turn down the screw spikes tight on the rail, but this resulted in a movement of the spike in the tie affecting the serviceability of the construction. The 1/16-in. space between the head of the screw spike and the flange of the rail has overcome this difficulty.
Only two types of screw spikes are used in our work. Screw spike "A" is the standard track spike for concrete track, while screw spike "E" is used principally for rail braces in curved track and in special work. The accuracy of the manufacture of the screw spike is of the greatest importance ; first, in order that the space between the head of the screw spike and the flange of the rail may be maintained, and second, that the groove formed in the wood of the tie block with the first thread of the screw may be followed by the remaining threads in such a way as not to injure the fiber of the wood. In replacing screw spikes, the groove in the wood should be followed by the threads of the new spike. These conditions are not met in the so-called "commercial" screw spikes.
Service requirements necessitate a substantial form of guarded construction consisting of rail braces on the outside of the high rail, and rail braces on the inside of the guarded rail on the low side. Guard rails are secured to the running rails by bolts passing through separators, separators being needed to provide the necessary flangeway. Although the separator bolts have been placed at frequent intervals, there has been a large amount of breakage under traffic. Several special designs have been developed to obviate this difficulty, but to date none has been tested on our rapid transit lines. The operating companies have been experimenting with the use of guard rail clamps similar to those commonly used opposite frogs on steam railroads. However, these are expensive and clumsy and not well suited for use on concreted track, as they require the omission of a large amount of concrete between the tie blocks.
In our new design we are seeking to minimize this difficulty by providing bolts manufactured to a special specification which will have greater elasticity and will be less liable to breakage. We are also modifying the design of the separator, providing a larger hole for the bolt, and have adopted a headlock washer which has shown good results.
Rail creepage has in the past been the cause of a great deal of difficulty in maintaining tracks, and the use of anti-creepers to overcome this trouble has been the development of comparatively recent years. On the first subways no anti-creepers were used, but when work was started on the tracks for the dual system three anticreepers to the rail length of 33 ft. were adopted as standard. Under actual operating conditions, this number of anti-creepers was found to be insufficient to hold the rail, necessitating a considerable amount of maintenance work which often required bucking of rail for a long distance. As the result of this experience, for the last few years we have used five anti-creepers to the rail length, which has proved satisfactory. In general, experience indicates that rail creepage occurs in the direction of traffic, more or less regardless of grades. Determinations in this matter are the result of intensive surveys which we have made of tracks under operation. On account of the high cost and great difficulties involved in making renewals it has been the uniform practice to provide ties manufactured from a very high class of material. For the ballasted track, including the special work, our specifications call for first growth, long-leaf. Southern yellow pine. No tie is acceptable with less than three heart corners, or with more than 1 in. of sap on the fourth corner or with more than 2-1/2 in. of sap, measured across the face anywhere in the length of the tie. Variations up to 1/4 in. in width and depth and up to 1/2 in. in length are accepted. These ties are delivered cut to the correct dimensions. Standard 6x8-in. ties 8 ft. long, and ties 9 ft. long for the support of the third rail, are used, with ties of various lengths as required for special work, which in some cases run up to 27-1/2 ft. in length.
For the concreted track, as described in an article published in this paper Feb. 2, creosoted timber is used of the same quality as for ballasted track. These ties are furnished to exact dimensions 10 in. wide and 6 in. high, with holes drilled for screw spikes, for anchor bolts where used, and for lag screws used for fastening the third rail insulator cups and brackets. The holes are exactly spaced by template prior to creosoting.
Long life is expected for these ties, based upon the present condition of similar ties which have been in service for about twelve years. A recent inspection shows little deterioration, and practically no tie cutting or failure in the screw spike holes. Because the ties are protected from extreme weather conditions it may be expected that deterioration from decay will be slow, and on account of the use of practically all heart timber, comparatively light wheel loads and the use of tie plates, there has been practically no deterioration from tie cutting.
On tangent and long radius curves, unused holes in the tie plates make it possible to drill new holes in the tie blocks after the first holes are unserviceable. In the case of sharp radius curves, where due to double spiking and other reasons it is impossible to provide spare holes, this cannot be done. However, the use of ties 10 in wide with tie plates 7-1/2 in. wide renders it possible in future to plug old holes, shift the tie plates, and drill new holes.
Standard frogs and switches are used wherever possible in our special trackwork. However, the many limiting conditions of the alignment necessitate the designing of numerous non-standard layouts. The greater part of our special work is of much sharper curvature than on steam roads and consists of No. 6 and No. 8, with some No 10 and No. 12 turnouts of radii from 350 ft. to 1,350 ft., whereas in the case of high-speed crossovers on steam railroads the numbers run anywhere from No. 12 to No. 20 and even No. 30, with very few under No 12. As a result we provide a large amount of guarding through the special work, which is not required ordinarily in steam railroad practice. Our switches are double housed for facing switches and single housed for trailing switches, with guards in front of the housings. Switch points up to a No. 8 are guarded on the turnout side. The wing rails of frogs are extended by guard rails. For the dual system, lapped switches have been used on the Interborough lines, with guards opposite the extended points, whereas on the Brooklyn-Manhattan lines housed switches have been used. We are following the Brooklyn-Manhattan practice in this regard for the new city subways. The use of the lapped switches for the Interborough lines was based on the contention that the rolling stock is so designed that with extreme rail and wheel wear the equipment on the under side of their cars would not clear the housing, which extends 1/4 in. above the top of new rail. Our new cars are similar to the Brooklyn-Manhattan Transit cars in having clearance between the equipment and the rail.
Rail built-up frogs are standard for our work. After years of service these frogs have proved entirely satisfactory and are particularly advantageous from the point of view of repairs under service. We have in a few instances installed solid cast manganese frogs. These have been in track for three years and are being watched in service. However, they are open to the objection of difficulty in repairs under operation in case of breakage. The advantage of the use of housed switches, especially for subway tracks, consists principally of more guarding at the extreme points of the switches. In this form of construction there is an offset in the stock rail, which makes it possible to thicken up the switch point, thereby adding to its stability and life.
Rolled manganese rail is used in special work for parts that are subjected to hard service, especially frogs for main line. Where it is necessary to provide for very frequent train movements, switch points and curved lead rails of rolled manganese are also provided.
For the dual system the third rail, bonding and insulated joints, as well as signal interlocking, etc., were installed by the operating companies as equipment, while for the new city subway all this work is being done by the city. The installation of the third rail, bonding of the third rail and installation of the insulated joints and of conduits in the trackways are all included in the track contracts. The track contractor's equipment for handling materials is suitable and available for handling the third rail, and the work can be carried on to advantage by him in connection with his track work. The necessity of providing for positive and negative cables, lighting, escalators and circuit breaker connections require that a large number of conduits be placed in the trackways. These conduits must, of course, all be placed in advance of the concreting. Delays and interference are reduced to a minimum, due to having all of this work executed by one contractor.
In general, the standard section of the third rail is 150 lb per yard of special section, with the third rail protection boards supported by brackets from the tie blocks extended for that purpose. The insulated joints are installed in the tracks at the time of track-laying.
Double housed switches, as used on the B.M.T. and new subway lines.
[Top] Joints at unguarded rail showing B bars. [Bottom] Joints at guarded rail showing F and G bars.
[Top] Separator and tie plate H for screw spikes. [Bottom] 150-lb. third rail with bracket and insulator.
Lapped switches, as used on the Interborough Rapid Transit Lines.