Signal System

A Description of the Automatic Block Signals Installed on a High-Speed Electric Railway Using Alternating Propulsion Current. An Account of the Interlocking Plants and of the Telephone System is Included.

Published in Electric Railway Journal,
Vol. XL, No. 3, July 20, 1912.

New York, Westchester, & Boston; Signal System- View of a Four-Track Signal Bridge Showing Platforms and Protective Screens

The New York, Westchester & Boston Railway, a new suburban line of which descriptions have been given in the Electric Railway Journal of June 15 and previous issues, 15 a single-phase electric road which extends north from New York City, with a four-track section approximately 7 miles in length dividing at Columbus Avenue into two double-track branches. One of these extends eastward approximately 2 miles to New Rochelle and the other continues about 9 miles north to the city of White Plains. The construction of the road throughout provides for the heaviest kind of suburban traffic with multiple-unit cars having a normal maximum running speed of 57 m.p.h.

Stations on the four-track section and on the New Rochelle branch are at intervals of approximately 1/4 mile and at intervals of 1 mile on the White Plains branch. Express stations are approximately 21/4 miles apart. The average train speed, including stops, is 37 m.p.h. for express trains and approximately 22 m.p.h. for local trains, and it is expected that the ultimate schedule will necessitate a five-minute headway for both classes. To handle such a traffic with safety and without delays it was necessary to install not only a block signal system of thorough reliability but also a communication system between stations and between the interlocking towers at switches, which would be rapid as well as free from possibility of failure.

To avoid the possibility of unsatisfactory operation due to the use of different pieces of apparatus which might not work harmoniously together if furnished by different contractors, the complete system of automatic block signals, together with the seven interlocking plants, was installed under a single contract by the Union Switch & Signal Company. For the same reason the system of intercommunicating telephones was furnished complete by the Western Electric Company. Both systems were planned and worked out in detail in the offices of the railway company under the direction of John Roberts, engineer of maintenance of way, and M. H. Loughridge, office engineer, the conventional wiring diagrams and curves accompanying this article and showing the novelties in the electric circuits for different functions being specially prepared in the office of Mr. Loughridge.

Principle of Operation

As with other systems of automatic signals for double-track lines the road is divided into sections or blocks about 4000 ft. long, insulated from each other to permit the rails in each to be used as an isolated electric circuit.

The operation of the signal system on the new line is, however, complicated by the use of 25-cycle single-phase propulsion current delivered from all overhead contact wire at 11,000 volts. In consequence certain differences exist between it and the usual types of track-circuit signals installed on electric railways which use direct current for the propulsion of cars. The most important of these is the use of a frequency of 60 cycles for the signal current in combination with 25-cycle propulsion current, in order that the increased inductive effect of this frequency over that produced by the 25-cycle propulsion current would permit the installation of positively acting devices responsive only to the action of the signal current.

The operation of the signals is effected by feeding a 60-cyc]e single-phase current supplied from an exterior source into the rails at the center of each block. The power thus applied amounts to very roughly 0.1 kw per block, depending upon the block length, leakage between rails and other influences, reaching the track relays with a value of about 4 amp and 3 volts. It is, however, the only source of energy used to operate the track relays, which in consequence are exceptionally positive in action. From one rail it passes through the track relays at each end of the block into the other rail and back to the other supply circuit connection in the center. This is shown diagrammatically in the accompanying cut of a conventional track circuit for one block. Whenever a pair of car wheels rests upon the rails at any point in the block it offers a path of much lower impedance than is exerted by the normal circuit, which, as shown by the dotted-line arrows on the sketch, includes the highly inductive track relay. The result is that the track current follows the path of least impedance and ceases to flow through the coils of the track relay. The latter normally holds closed a circuit upon which is the motor for operating the semaphore. When the track relay is first energized this motor starts and raises the signal counterweight so that the semaphore arm goes to clear position. The arm is held in place by a latch which is kept engaged by a so-called "slot magnet" so long as current flows through the coils of the latter. When a train enters the block the track relay is de-energized, and the signal circuit is broken. This results in de-energizing the "slot magnet" and releasing the latch which has been holding up the semaphore counterweight. The latter falls by gravity as soon as the latch is released, and in consequence the signal moves to danger position. When the train leaves the block and the short-circuiting effect of the car axles is removed the track current reverts to the original path along one rail through the track relay and back along the other rail. This energizes the track relay which in turn closes the signal circuit and permits current again to flow through the signal motor and slot magnet at the signal mast. In consequence the signal motor starts to revolve and raises the signal counterweight, lowering the semaphore arm to the clear position. In this position the latch engages and is held in place by the slot magnet until the signal circuit is again opened by the passage of another train.

Impendance Bonds

The isolation of the track circuit formed by each block is effected by the usual fiber-insulated rail joints at the ends of each block. To provide a means whereby the rails can be used as a return for the propulsion current, the ends of adjoining blocks are connected together as shown in the accompanying cut of a conventional track circuit. These connections or impedance bonds take the place of the customary cross-bonds and are installed in pairs, one on each side of all insulated track joints. Each consists of a coil wound upon an iron core, and each pair of bonds are connected together at the centers of their coils. The propulsion current enters the coil from both ends or from each rail, and leaves the coil through the center connection, passing to the other coil of the pair and then to the rails of the next block. In this way two opposing magnetic fields are set up, one in each half of each coil, which, when the intermediate joint bonding in both rails is equally good, are balanced in strength and neutralize each other. Since the iron core under ordinary conditions is demagnetized the energy loss due to the passage of the propulsion current is negligible.

On the other hand, the highly inductive nature of the bond acts as a choke to the alternating signal current and only permits a negligible amount of this current to pass through it from end to end or between the two rails. In consequence the track-circuit current is shunted through the track relays.

The bonds are made with laminated iron cores and are shaped like a shell-type transformer. The windings which surround the center member of the core are made of heavy strap copper and have a capacity for 200 amp. The whole is submerged in transformer oil. The cast-iron boxes containing the bonds are set between ties and practically level with the top surface of the ballast. Connections between the boxes and rails are made of No. 0000 bare copper strand, and as the rail joints are staggered one leg has to be extended half a rail length to the nearest opposite rail joint. This leg is carried in a wooden trunking below the ballast.

Track Relays

The track relays which make or break the signal circuits and are connected in series with the track circuit are located at each end of each block. These relays are energized solely by the track circuit in contradistinction to the types which depend for action upon the effect of current from an exterior source in combination with that from the track circuit. With the former type the flow of current in the track circuit is considerably increased, and this greatly increases the short-circuiting or shunting effect of several pairs of car wheels resting on the rails of the block.

Current for the track circuit is fed into the center of the blocks instead of into one end in order to introduce the impedance of the rails between the point of supply and the impedance bonds at the ends of each block. The impedance drop due to the rail reduces the voltage impressed upon the impedance bonds, and consequently tends to minimize the proportion of the track circuit current which is shunted through them and thus fails to pass through the track relays. If the block was fed at one end and one track relay located at the other end a heavy current would be shunted through the bond at the feeding end, as the impedance of 4000 ft. of rail is a very material item when opposed to the impedance of the bond. An advantage of having the feeding points located at the center of the block Instead of at the end is that in the latter case the presence of a stationary train held by a signal would cause a considerable waste of power, as its wheels might be directly over the feeding points for considerable periods of time. With center-fed blocks the trains which stop at the ends of the blocks have interposed, in the circuit, the impedance of some 2000 ft. of rail, and this materially reduces the flow of current.

Two relays are required for each track circuit on account of the center-fed blocks. If only one relay was used the impedance of the rail between the feeding point and the end opposite to that on which the track relay was located would be so great that when a train was at that end of the block enough current might still be shunted through the track relay at the other end to hold the signal circuit closed. The presence in the block of a pair of wheels only short-circuits the rails and does not, of course, short-circuit the supply.

The track relay or frequency relay is of the vane type, which takes advantage of the moving field effect produced by shading coils. Its construction is shown diagrammatically by a plan view in the cut of the track circuit. The field is produced by a coil on a double-tee-shaped core and, in the air gaps formed by the spaces between the arms of the tees, oscillates a double aluminum vane which in elevation looks like a "U" with very wide arms. The vane is fastened at the bottom to a yoke which pivots on centers in the frame supporting the core, and this permits the vane to oscillate freely in the air gap through an angle of about 45 deg. The centers on which the vane pivots are located on the center line of the coil on the core. On the axis of the vane is a short crank and an arm, which is connected to a contact spring carrying a carbon contact. When one side of the vane swings up this contact makes a connection with a metal strip on one terminal post of the relay. When the other side of the vane swings up and the former side moves down the contact recedes and the connection is broken. The contact spring is connected by a flexible cable to the other binding post of the relay so that the vane opens or closes a circuit according to the direction of the swing of the vane.

The impedance bonds previously described are normally intended to receive exactly one-half of the return current at each end or from each rail, discharging the whole current through the center connection. This, however, would necessitate an exactly equal resistance in each one of the two rails, and such a condition, due to slight defects in bonding or other causes, is a practical impossibility. When a larger return current flows in one rail than in the other a portion of the excess will be shunted through the track relay to the rail carrying the smaller current, and the disturbing effect of this unbalanced current has to be provided for by making the relay so that the normal flow of 60-cycle signal current not only holds the signal circuit closed but will hold it closed regardless of the presence of any reasonable amount of propulsion current. This condition is effected by making one side of the relay most sensitive to 25-cycle current and the other side to 60-cycle current, the two sides exerting opposing pulls upon the vane.

As shown in the drawing, the frequency relay has shading coils surrounding one-half of each pole face. These shading coils are in the form of copper ferrules, and as the direction of the magnetic field is reversed each time the alternating Current reverses in the field coils of the relay, induced Currents are set up in the shading coils. As the magnetism in the coil rises, at the beginning of a cycle of the primary Current, the induced current in the shading coil tends to retard the flux in the shaded portion of the pole face, and as the primary magnetism begins to decrease preparatory to reversal the induced Current in the ferrule tends to maintain the flux in the shaded portion. The same thing happens after reversal, and in this way the intensity of the flux is continually shifting its position from the unshaded portion of the pole face to the shaded portion. In effect there is a moving field which draws the vane with it.

At one end of the relay the pole faces are enlarged, and a choke Consisting of another copper ferrule surrounds the entire pole. The result is that the pull of the field set up by 60-cycle current alone is less than at the other end, and if 60-cycle Current only is impressed on the relay the side of the aluminum vane between the small pole faces will be raised up. If, however, only 25-cycle current is impressed upon the relay the choke is less effective on account of the lower frequency, and the enlarged pole faces produce a greater pull, with the result that the side of the vane which is between them is raised. When both 25-cycle and 60-cycle current are impressed the vane takes a position in accordance with the field of greater strength.

When the relay is normally energized with 60-cycle signal current it will stand from 9 amp to 12 amp of 25-cycle propulsion current through its windings before it will open, and owing to the small return currents existing on account of the high-voltage transmission system, together with the auto-transformer action of the impedance bonds tending to balance the circuit, such an effect could be produced only by a very bad power bond or a broken rail. In either of these cases the signal would go to danger position and remain there until the defect was discovered and remedied.

End-fed single-rail track circuits are used for the short sections of ladder tracks in switching yards, one rail being used for signals and one for power return. The power return rail is continuous through the interlocking. The circuits are fed through a resistance from one transformer connected to the 110-volt a.c. supply and stepping the voltage down to that required for operating the track relays. This is the first installation, in connection with a.c. propulsion, of single rail return and signal circuits.

The relays along the line are enclosed in wooden boxes which have hard rubber panels for the terminals and fuses. A lamp socket is provided in each for use with a portable lamp in case examinations of the relays are required at night.

Signals

Since the new line uses the tracks of the New York, New Haven & Hartford Railroad for reaching its New York terminal, signals similar in aspect to those of the New Haven System were considered preferable to three-position signals. For this reason two-position semaphores are used, most of them being suspended from the catenary bridges. The semaphore arms are center pivoted, counterweighted to return by gravity to the horizontal, and have a movement of 60 deg. from this position. They are located with a minimum clearance of 15 in. from the pantographs on the cars and are operated on the "normal clear" principle.

Interlocking Tower with High and Dwarf Signals at Turn-Out

All high signals are controlled by the Union Switch & Signal Company's "Style B" mechanism, adapted to alternating-current operation. The accompanying half-tone shows the mechanism for a single semaphore controlled from an interlocking plant. This is exactly similar to the automatic block signal operating mechanism except that in the latter the indication circuit controller is omitted. The indication controller is the switch showing at the right-hand corner of the casing and connected by a small vertical rod to the slot arm. Its function is to open or close a circuit which operates the indication magnet for the segments of the signal lever in the interlocking tower. Thus it permits the signal lever to complete its stroke and release the mechanical interlock on the switch lever governed by the signal only after the semaphore arm has actually moved into the stop position corresponding to the normal position of the lever. Double-arm semaphores have duplicate slot-arms operated by the same motor and transformer, the motor operating the two slot arms by two endless chains on the same shaft.

The connections for a signal are shown in the conventional diagram of a signal circuit. By comparing this diagram with the half-tone showing the signal mechanism it will be seen that the motor indicated in the cut is located at the bottom of the mechanism casing. The slot arm and slot magnets are located immediately above the motor and are raised by the movement of an endless chain geared to the motor, the chain having a trunnion on one of the links which engage with the triangularly shaped fork at the end of the slot arm. When the slot arm reaches the top of its stroke a spring latch engages with a lug on this fork and holds. in this position the slot arm, together with the heavy push rod attached to it and extending up through the signal mast to the semaphore counterweight. At the top of its stroke the slot arm strikes the contact arm shown near the top of the casing and opens the contact points. This contact corresponds to one of the three switches shown in the conventional diagram just above the motor.

The fork or toggle at the end of the slot arm is pivoted to it and held in rigid alignment with the slot arm by bell cranks extending back to the slot magnets. When the slot magnets are de-energized the toggle is no longer held rigid with the slot arm, and by swinging on its pivot is disengaged from the spring latch, with the result that the slot arm falls down into the bottom position or that shown in the halftone. The slot magnet also acts as a relay, closing, when energized, the motor circuit, as shown at the upper left-hand portion of the diagram. Thus, in the normal condition which begins after the passage of a train, the slot circuit is closed by the track relay. This results in first holding rigid the toggle at the end of the slot arm and second in closing a circuit through the signal motor. The latter circuit remains closed until the slot arm is raised and the signal cleared, at which time the circuit is opened by the slot arm striking against the contacts at the top of the mechanism and separating them. The latter condition is shown by the position of the switches in the conventional diagram. In consequence the motor stops but the slot magnet remains energized and holds the slot arm up and the semaphore in clear position until the passage of a train breaks the circuit at the track relay.

In the upper right-hand corner of the casing is shown an air dash pot which is connected to the slot arm to prevent shock when it is released and falls into danger position.

The motors for all signals are of the single-phase type without a commutator. They will start automatically from any position and will operate the blade through a complete movement in four seconds.

Dwarf signals, which are used for slow-speed train movements in reverse from the normal direction of traffic, are of the solenoid type, operated by direct current at 110 volts and controlled by a local a.c. relay which takes the place of the slot magnet on the high signals. In the subway section of the line, which extends about 4000 ft. north of Morris Park, light signals are used similar to the night indications of the block signals. All signals are electrically lighted with 2-cp, 2.5-watt tungsten filament lamps. These are operated by transformers on the 110-volt signal circuit, which steps the current down to 12 volts in order to give the highest possible lamp efficiency. Two lamps connected in multiple are used for each signal light.

No wires are common to more than one source of energy, limiting the maximum length of wire to that of two blocks. This reduces the inductive influence from the propulsion current and simplifies maintenance, although it increases somewhat the necessary number of wires.

Signal Location

The block signaling was worked out on the principle that when approaching a stop signal the motorman should have an advance indication in proper time to stop his train when traveling at maximum speed, before reaching this signal. The retardation with the service application of the braking equipment was assumed as equal to a reduction in speed at the rate of 11/2 m.p.h.p.s. on level track, although the emergency braking application will cause almost twice this rate. The cars are fitted with a speed controller which cuts off the power from the car motors when the speed exceeds 57 m.p.h. This speed may, however, be accelerated by coasting on descending grade to 62 m.p.h. The braking curve showed that this advance indication, where trains attain maximum speed on level track, should not be less than 1820 ft., and on a 1 percent descending grade should not be less than 2200 ft.

It was assumed on account of the limiting condition of foggy weather that the indication of the distant signal would be read when the train is at the signal. The braking distance, therefore, was lengthened to such an extent as would give the motorman ample time to act on the indication and prepare to stop at the next signal. The extent to which the blocks should be lengthened for this purpose involves the personal equation of alertness in the motorman. To provide a factor of safety the blocks are arranged at approximately 200 percent of the service braking distance, which at maximum speed allows the motorman an interval of twenty-one seconds after passing the signal in which to apply the brakes. The usual practice was adopted of combining in one signal the advance indication for the succeeding block with the stop indication and with the braking distance, as determined above, the blocks were arranged for the closest headway.

In most signal installations of this kind the theoretical length of block can only be approximated in practice. But on this road the interlockings are so located that fortunately the distance between them approximates a multiple of the length of block. In a number of cases, however, the signals had to be so located as to clear the platforms at passenger stations.

The maximum length of block cannot be uniformly applied to advantage on account of variations in speed. All scheduled trains stop at express stations, and only at points between these can maximum speed be attained. Moreover, there are certain curves and viaducts where a limited speed is called for. At the passing sidings, which are 1500 ft. long, the rear distant signals indicate for both the interlocking signals at each end of the siding, and a train must travel this additional distance before a clear signal can be obtained for a following train. These conditions call for a shortening of the block so that trains may close in, and they have been shortened as far as a safe operating margin for non-stopping trains at these points would permit.

The signaling on the local track for reasons of economy has followed the same arrangement as on the express tracks, although the average speed is considerably less.

In practice an average headway of two minutes and twenty seconds is possible for express trains and three minutes and forty-five seconds for local trains, including stops, and at no point is the possible headway for the latter greater than five minutes and six seconds. A time-speed curve is shown for express trains from East Third Street station to Wykagyl on the White Plains branch. The signals are spaced on this curve according to the time that the train takes in running through the blocks. The headway is equal to the time required for a train to run the length of a distant signal indication plus the time required to run its length and eight seconds for the movement of two signal blades. This curve also shows the speed of trains at any signal location.

Considerable thought was given to the use of automatic stops. and although it was decided not to install them initially, their future use was considered of such importance as to make it desirable in the present arrangement to provide the necessary parts of the apparatus for this purpose. Their use requires overlapping the control of the signals, which always secures a space interval between trains equal to the length of the overlap. On this account the factor of safety on the braking distance can be very materially reduced, and in fact was taken at 40 percent instead of 100 percent, as in the present arrangement.

From a construction point of view the ideal arrangement for future overlaps would be to place an additional signal in the center of each of the present blocks, thus reducing the distance between signals by half. If this was adopted, however, it would be necessary to reduce the maximum allowable speed. But without restricting the speed the present signals may be closed in on account of the reduction in the margin of safety (by 60 percent), and by additional signals a headway that will meet the requirements of the ultimate schedule may still be maintained. An arrangement of this kind has been worked out which will call for the relocation of thirty-two signals and the addition of thirty-six blocks. This will permit the same average headway for express trains and will increase the headway for local trains by ten seconds. The power for the system has sufficient capacity to operate these additional signals. This, it may be said, is the first time that a complete block signal system of this character has been planned with a view to the future installation of overlaps for automatic train stops.

Frequency Changers and Switchboard in Substation

Substation for Signal Current

Power for operating the signal switch and track circuits is obtained primarily from the main feeders carrying the propulsion current. The signal current, however, is delivered at 60 cycles in order to permit selective action on the part of the track relays through which the propulsion current at 25 cycles as well as the signal current is liable to be passed. This necessary difference in frequency is obtained by the use of frequency changers, consisting of a 60-cycle, 2200-volt, 720-r.p.m. single-phase generator of 45-kw capacity mounted on the same shaft and driven by a three-phase induction motor. The latter is of 75 hp capacity and receives its power from the main feeders and from a third phase wire which is carried along the line of the railroad from the main power station at Cos Cob. Current is delivered to the motor at 440 volts, being stepped down by transformers on the 11,000-volt feeders. These transformers are located in a high-tension room occupying the two-story portion of the substation building. In order to steady the load as well as to provide a power reserve a 70-hp, d.c. shunt-wound machine, operating at 160 volts and upon which floats a 400-amp-hour battery, is mounted upon the same shaft with the frequency changer. This operates as a motor running upon the storage battery or as a generator feeding into it in accordance with the rise or fall of the load. The battery alone will carry the entire load of the station for one hour.

The pressure of the signal mains is kept constant at 2200 volts by means of a Tirrill regulator on the field of the direct-connected exciter for the single-phase generator. A field regulator on the d.c. machine automatically maintains the speed without regard to the fluctuating voltage supplied by the storage batteries in case it is necessary to operate with them alone. A circuit-breaker which trips both on overloads and underloads is installed to protect the batteries, and the customary time-limit relays are used for protection against overload on both sides of the frequency changer, together with a relay which trips the oil switches with a low voltage at the supply mains. All of the apparatus for supplying the signal system with 60-cycle current was furnished by the General Electric Company.

Signal mains of No. 3 B. & S. gage bare copper strand are carried in duplicate on the catenary bridges. All apparatus is connected to one of these circuits which is divided into sections to permit repairs without interruption of the whole line. The other circuit is used as a feeder. Wooden platforms are carried level with the bottom chord of the catenary bridge trusses which carry signals, and these are provided with trap doors for access to the semaphores suspended below. Pipe railings are provided along the platforms, and the high-tension wires above them are protected by wire screens. The transformers to the signal circuits are located on the catenary bridge truss, and those for the track circuits are housed in dust-proof cast-iron boxes adjacent to the bridge columns.

Substation for Generating Signal Current

Wire protection has been carried out to an unusually complete degree. Kerite insulated wires and cables are used throughout except for the 2200-volt signal mains carried on the catenary bridges. Wires exposed above ground, as well as the lead-covered high-tension connection to transformers, are enclosed in iron conduit. All underground wiring is run in fiber conduit laid in concrete. A four-duct conduit line is installed along the center line of the railway, being made up with fiber ducts at the fills and tile duct along the cuts. This is installed primarily for the telephone system, but one duct is used for the signal circuits between blocks. Manholes are provided at the signal bridges and as required along the conduit line. Connections for switch movements where vibration exists are protected by flexible armored conduit, and distributing boxes for connection to different parts of apparatus are provided generally with screw covers or other forms of dust-proof handholes. This all results in the elimination of unslightly wood trunking and assures a low rate of depreciation on the wires.

Interlocking

Seven power interlocking plants are installed for the operation of main-line switches. Power operation was essential for the frequent movements necessary at the larger plants and was installed in the small plants on account of the lower cost of installation compared with mechanical interlockings as well as the advantages in using uniform apparatus.

New York, Westchester, & Boston; Signal System- Tower and Substation at Columbus Avenue Junction

The interlockings are installed with the safeguards usual for high speed and dense traffic. Approach locking insures the integrity of the route to a train that has received a clear signal, and this cannot be changed for an interval of one and one-half minutes. An emergency release, however, is provided in the junction and terminal towers, enabling the leverman on breaking a seal to release instantly the approach locking and change the route in cases of emergency, the breaking of the seal requiring an explanation as to the cause. Route locking secures the route in front of the train when it is within the limits of the interlocking after the signal lever has been restored to normal. The locking of the switches, however, releases as soon as the train has passed over them. Separate indications are provided for the approach of trains in each of the two blocks in rear of the first home signal so as to give separate indications for trains following each other one block apart. These indications consist of lights in a model of the tracks placed over the interlocking machine and a buzzer calling attention to the lights. Light indicators are also provided to show when the signals may be cleared and when the detector switch locks are released. Thus signalmen have ample indications of approaching trains, of the route that may be set up and of the signals that can be cleared, these latter indications being embodied in the interlocking machine.

In the small interlockings where it is not necessary to have a leverman constantly in attendance the signals for the direct movements operate automatically the same as block signals when the lever controlling them is kept reversed. Thus through trains may pass these interlockings without attention on the part of the operator.

The most congested interlocking is the junction at Columbus Avenue on account of the grade crossing for the New Rochelle express and the White Plains local trains, and of locals from New Rochelle which cross with expresses from White Plains. Train movements at this place have to be made with the utmost dispatch. This is because the express station at East Third Street, Mount Vernon, has been selected as the starting point of the timetable, which has been so drawn that passengers may transfer between express and local trains in both directions without delay. It is further planned that a White Plains local shall arrive with a New Rochelle express and a New Rochelle local with a White Plains express. The operating margin in the former case is shown in the curves on the accompanying diagram. Assuming that the express and local trains leave at the same time, the trains move together until the local slows up for the stop at Columbus Avenue station. In this time the express for New Rochelle must gain sufficiently to clear the interlocking and enable the route to be cleared for the White Plains local before the latter arrives at the interlocking signal on Bridge 115. In the cut an eight-car express train and a five-car local train are shown in their relative positions at the speed allowable. This curve shows that there will be a margin of 11.5 seconds in which the interlocking signal may be cleared before the local train reaches it.

Interlocking Apparatus

The interlockings are operated by the Union Switch & Signal Company's type "F" all-electric system. Switch movements are of the motor-driven type in which a horizontal drum operates the necessary cranks. Switch motors are connected through a friction clutch and reduction gearing to the switch points. The switch controller is set on a concrete foundation beside the switch and enclosed in a weatherproof case. This operates in response to the movements of the interlocking lever which controls the switch movement, and by changing the direction of the current through the switch motor armature it controls the direction of the movement of the switch. Additional contacts on the controller cause both ends of a cross-over to move simultaneously.

The accompanying wiring diagram shows conventionally the circuits for the interlocking of a single switch. At the right is the switch controller, which in effect is a motor capable of making one-fourth of a complete revolution and whose armature swings either way in accordance with the direction of the current in the field coil. Next to this is the switch motor and its field, and to the left of this is shown the indication circuit controller which controls the normal and reverse indicating lock on the lever. This is attached to the locking bar of the switch movement, and consequently is shifted when the switch has completed its movement. The batteries are shown at the extreme left, and the circuit connections, which are closed at different positions in the movements of the lever, are indicated by the lettered circles, corresponding to the lettered positions in the conventional diagram of the lever. The two segments on the locking shaft which control the movement of the lever from the normal position to the reverse and vice versa are below, together with the indication magnets which are to be energized in order to permit the jaws on their armatures to clear the teeth of the segments as they are moved by the lever. Energy for the various locking functions is supplied through the d.c. bus mains shown at the bottom of the cut. In addition to these, as shown, only four wires are required between the lever and the switch, of which two are connected to the field of the switch controller and cause it to move in accordance with the direction of the current in them. The other two wires extend from the indication circuit controller to the indication lock on the lever.

At the right of the locking shaft segment is shown a safety relay which can only be energized and thus give a clear signal when the position of the switch and lever correspond. This is inserted in the circuit controlled by the signal lever, and in case the mechanical interlocking between the switch lever and its corresponding signal lever permits the latter to be moved to a position which should give a clear signal the signal circuit will be open and the signal itself will not clear unless the switch has actually followed the movement of the switch lever. Direct current for operating the switches and interlocking functions is furnished at each interlocking tower by a motor generator set floating on a storage battery. This receives power from the signal mains through duplicate transformers which step the voltage down to 110 volts.

Telephone System

A telephonic communicating system between dispatchers, interlocking towers, and stations has been installed, and on account of the necessities of the high speed and dense traffic has been designed with unusually complete provisions against breakdowns as well as delays in establishing communication. These safeguards are effected by installing a number of different circuits, assigned to the various services and connected through different stations or towers so that all communicating points of any importance can plug into either one of at least two of them. Points of unusual importance can plug into any one of five different circuits, so that the possibility of delay on account of wires being in use or broken is so remote as to be negligible.

The road is to be operated from the general offices in New York City, and at that point is a telephone switchboard of the ordinary commercial type with a capacity of thirty lines. At this board all circuits can, of course, be interconnected as desired, and at night when the executive offices are closed the lines can be left by the operator so that all points on the road are in direct communication with each other. This may also be done by the tower man at the Columbus Avenue junction, but under these circumstances there is no indication when communication is ended and the line is clear.

Telephone Circuits

The circuits, which consist of twisted pairs of No. 10 gage paper-insulated copper wire in lead-covered cable of low electrostatic capacity are arranged as follows: a train wire connects all interlocking towers on the four-track section and the New Rochelle branch. A second train wire connects all interlocking towers on the four-track section and the White Plains branch, these two wires being so arranged that they may be handled together by one dispatcher or separately by two dispatchers. A local wire connects all stations on the four-track section and the New Rochelle branch, and a second local wire connects all stations on the White Plains branch and the express stations only of the four-track section. A through message wire connects the chief points, such as interlocking towers, express stations and terminals, on the whole road. There is in addition a line between all interlocking towers with which towermen may communicate without using a through line. This is intended for use with a future train-describing system.

Each of these circuits is numbered and a diagram is provided to show upon which one it is necessary to plug in at any station in order to obtain direct communication with any other station without the assistance of the switchboard operator in New York City.

Additional lines which can be substituted for defective wires in the circuits, or which can be used for special conditions, are also provided over the entire road. All lines including spares, are brought into jacks at each interlocking tower so that substitutions of sections of sound wires for defective ones can be made without breaking connections.

Where distances between stations exceed 1 mile, outlying telephones are provided so that track-walkers do not have to travel over 1/2 mile to report trouble. General accessibility for trainmen is provided by telephones located on station platforms at all express stations and at alternate local stations.

With this arrangement the number of stations on any circuit does not exceed twenty, and the greatest number of stations on any line not having an alternative speaking circuit is ten.

Each communicating point is given a double number, of which the first part indicates the number of impulses sent out by a stepping wheel set in motion when a call is made, and the second part consists of one of five additional-step numbers following a continuous impulse sent into the circuit. In calling a station after an unused circuit has been located by plugging into the various lines available for communication, the call is made by setting the double index to the number of the station called and giving a turn to a calling key. This sets up a series of impulses which sets in motion a stepping wheel through a stepping magnet and establishes a local circuit for the indicating apparatus consisting of a light over the proper plug connection and a buzzer at the station called, the circuit remaining closed until the call is answered by pressure of a push button on the inter-calling key and the insertion of the plug at the latter station.

The establishment of the circuit and the consequent call causes a buzzing sound in the receiver at the station sending the call. This is known as the "answer-back," and establishes the fact that the call has been received. After completing the message the two parties merely hang up their receivers.

The train wires are used exclusively for dispatcher's use, and ordinarily communication with him is established by merely plugging into the line. However, if the dispatcher's receiver is closed up an audible buzzer establishes the call and the caller gets the regular "answer-back."

Power for the local sets is obtained from portable storage batteries charged when necessary from the substation at Columbus Avenue. A 550-volt battery for the selectors is located at the telephone switchboard and is charged from one of the interlocking system motor-generator sets.

The inductive effect of the alternating propulsion current is counteracted by frequent grounding of the telephone cable sheaths in addition to the shielding effect obtained by carrying the telephone cable underground. Lightning arresters located at every station are also provided to discharge the induced electrostatic charges before they reach dangerous voltages, and provision has been made for installing compensating transformers to induce differential currents in a spare pair of wires in each cable to nullify if necessary the effect of future power increases.

Underground Telephone Ducts

The cables, which are located underground for appearance and permanence as well as for reducing inductive effects are installed in quadruple ducts of 31/4-in. tile in cuts and of 3-in. American Conduit Company's bitumenized fiber at the fills. Both types of duct are encased in concrete having a minimum wall thickness of 3 in. The ducts follow the track grade except on levels, where they are laid to a drainage grade of from one-fourth to one-half of one percent.

Manholes are located every 500 ft., except on curves. where the spacing is reduced, and also as required for outlets of buildings and signals. Tile drains surrounded by loose trap rock are located under the concrete carrying the ducts, and the bottom of this concrete at fills is reinforced with 1/4-in. square rods to protect against uneven settlement. On bridges of the solid-floor type fiber conduit above the bridge waterproofing is used, and on other bridges 3-in. iron pipe conduit with an expansion joint at the bridge center is led through the concrete abutments and across the bridge. Manholes are elliptical, 4 ft. by 3 ft. in size and approximately 3 ft. deep. The openings are 3 ft. by 2 ft. 6 in. and have corrugated rolled-steel cover plates of light weight, secured by bolts to the concrete.