Wayside signaling system for railroad cab signals and speed control

A transmitter and a receiver are located at each junction location between adjoining track sections along a stretch of track for transmitting and receiving cab signal or speed control commands through wire loops laid in a preselected pattern parallel to and between the rails of each section. Train carried apparatus is selectively reponsive to the speed commands and to the pattern of the wire loops to control the movement of the train in the established direction through the stretch. A distinct directional frequency is transmitted from the selected entrance end of the stretch, when a train movement is desired, and is repeated at each wayside location through the wire loops to the exit end. The directional frequency reception at each location activates a filter output to selectively enable gating elements to connect the associated transmitter and receiver to the adjoining section loops in accordance with the desired traffic direction. The speed command transmission is selected in accordance with the advance traffic conditions. If the immediate advance section is occupied by a train, a restricted speed command is transmitted in the principal loop of the approach section but no command is applied to a second loop at the exit end which causes the train to halt prior to entering the next section. This prevents the overrun of sections by a following train and the inadvertent reception of a higher speed command intended for the preceding train.

BACKGROUND OF THE INVENTION 
My invention relates to a wayside signaling system for controlling cab 
signals and/or speed control apparatus carried on vehicles traversing a 
fixed roadway. Specifically, the invention pertains to a fail-safe wayside 
arrangement by which speed or cab signal commands are transmitted to 
railroad trains through wire loops load between and parallel to the track 
rails while retaining all the safety characteristics inherent in the 
transmission of such commands through the rails. 
Although the transmission of speed and cab signal commands through the 
rails of the railroad track is an inherently failsafe arrangement, due to 
train rail shunts, it does occasionally create or build-in problems, 
particularly in electrified rapid transit systems. The use of wire loop 
arrangements to carry such commands can eliminate many of these problems 
and disadvantages. Among the advantages of using the loop transmitting 
system are negligible noise in the transmitted speed commands induced by 
propulsion current, cab signal sneak paths through bond connections are 
not as probable, the train apparatus does not have to respond to such a 
wide range of cab signal intensity or voltage levels, and the 
complications of physical attachment through some type of track bonds to 
the rails is eliminated. A principle objection to the use of wire loops 
obviously is that the signal carried therein is not shunted by the train 
moving through the stretch. Therefore, a following train could receive the 
same speed command as the leading train in the same signal block. This 
problem may be overcome by application of a stop command, indicating a 
very low speed limit, in the loops in the approach section to an occupied 
track section and by a preselected arrangement of loops, i. e., their 
pattern and positioning. A relatively fail-safe pattern for such wire 
loops is disclosed in the copending patent application, Ser. No. 719,336, 
having a common assignee and filed the same date as this application by 
Thomas J. Bourke and Kenneth J. Buzzard for a Transmitting Loop 
Arrangement for Railroad Cab Signal and Speed Control System. 
Accordingly, an object of my invention is a wayside signaling system using 
wire loops for controlling cab signal or speed control apparatus on 
vehicles traversing a stretch of fixed roadway. 
Another object of this invention is control circuitry for cab signal 
transmitting loops along a stretch of railroad track which provides 
fail-safe operation of the speed control apparatus on trains traversing 
that track. 
Still another object of my invention is a train control signaling system 
for transmitting speed commands from wayside locations to control 
apparatus on trains traversing a stretch of track, using wire loops 
positioned in a predetermined pattern parallel to the rails of the 
stretch. 
A further object of the invention is a wayside signaling arrangement for a 
railroad cab signal and speed control system which establishes traffic 
direction through a stretch of single track and supplies speed commands to 
trains traversing that track in accordance with the established traffic 
direction, with all traffic and speed signals transmitted through wire 
loops positioned between and parallel to the rails. 
It is also an object of my invention to provide wayside control circuits 
for transmitting cab signal or speed control commands to trains traversing 
a stretch of single track in either direction, with train detection 
provided by track circuits but the speed commands transmitted through wire 
loops laid in a predetermined pattern between the rails, the control 
circuits being designed to provide positive train stops prior to entering 
an occupied track section. 
A still further object of the invention is a speed control system for 
trains traversing a stretch of railroad track in either direction in which 
the speed commands are transmitted through wire loops laid betweeen the 
rails for inductive pickup by train carried apparatus, the loops being 
positioned in a predetermined pattern and supplied with control commands 
in a manner to provide fail-safe operation of the trains in response to 
advanced traffic conditions along the stretch of track. 
Other objects, features, and advantages of the invention will become 
apparent from the following specification and appended claims when taken 
in connection with the accompanying drawings. 
SUMMARY OF THE INVENTION 
In practicing my invention, I utilize a wire loop pattern for transmitting 
cab signal and speed commands based on the loop patterns disclosed in the 
previously cited application Ser. No. 719,336. Specifically, the 
arrangement shown in FIG. 1 of this copending application is used but 
fully modified for two direction operation. In other words, the principal 
or first loop along the track center line is provided with an offset 
portion at each end of the track section. Also a second loop is used along 
the center line at each end of the section paralleling the offset portion 
of the first loop. The source and control apparatus for the cab signal and 
speed control commands at each junction between sections are selectively 
connected to the loops in accordance with the established traffic 
direction. That is, a cab signal transmitter and receiver are selectively 
connected to the loops at the established section exit and entrance ends, 
respectively. Signals used to establish traffic direction are also 
transmitted through the loops. Specifically, in accordance with a desired 
traffic direction, a first or a second direction frequency signal is 
transmitted from the selected entry end of the stretch and is passed by 
repeater units at each wayside location to the exit end of the stretch. 
This directional frequency signal is also received at each intermediate 
location by a directional filter unit responsive only to the corresponding 
direction frequency. The responsive filter unit, when activated upon 
receipt of a directional signal, supplies an enabling or gating signal for 
initiating the cab signal command transmission into the approach section 
loops and activating the receiver channels to receive and decode signals 
received through the advance section loop. The reception of the traffic 
direction signal at the exit end inhibits the transmission of the opposite 
direction frequency and also blocks the clearing of the opposing entrance 
signal into the stretch. At the exit end also, this traffic direction 
signal reception initiates the transmission of the cab signal and speed 
control commands into the first loop of the final approach section, that 
is, the section in which trains will be approaching the exit end. 
Trains are detected in each track section by a track circuit shown 
specifically as an alternating current track circuit using the commercial 
frequency source. Section occupancy is registered at one end by a 
conventional track relay and is repeated to the other end of the section 
to a track repeater relay controlled by transmitting the same track 
current frequency over the first loop of the section. This superposing of 
track circuit frequency current on the loop does not interfere with the 
cab or speed commands. At each intermediate wayside location, that is, at 
each insulated junction between two adjoining track sections, transmitter 
and receiver units are coupled to the first and second loops of each 
section by coupling units which are normally inactive gating elements. 
These coupling units or directional gates are selectively activated by the 
directional filters in accordance with the traffic direction signal 
received. For example, a pair of coupling units are activated under an 
existing traffic condition to transmit the cab or speed commands developed 
by the transmitting unit into the first and second loops of the approach 
track section in the established traffic direction and to connect the 
receiver unit to accept the speed commands from the first loop of the 
advance track section. The traffic direction frequency signal is passed by 
a repeater unit which is coupled between the first loops of each of the 
adjoining sections in a manner to bypass the coupling units. Each receiver 
unit passes the received speed commands to a bank of filters which act as 
decoders. These decoders distinguish between the signal characteristics 
received and selectively pass the signal to one of a bank of code 
generators. The code generators transmit a related signal command, 
normally the next higher or equal speed level, to the transmitter for 
modulation of the cab signal frequency and subsequent transmission into 
the approach track section loops. When a train occupancy in the advance 
track section is detected by the track circuit, the occupancy register 
relay, that is, either the track relay or the track relay repeater, 
deactivates the receiver unit and directly selects the lowest speed 
command to modulate the cab signal frequency for transmission into the 
approach section loops. 
The selected speed command is transmitted from the transmitter direct into 
the first loop in the approach track section. Normally the second loop 
also receives the same signal command. If the advance section is occupied, 
however, registration of such occupancy interrupts the transmitter 
connections to the second loop of the approach section. Thus, no signal is 
passed through the second loop and an approaching train halts within the 
selected offset length. This is possible since, under the occupied 
condition of the average section, the lowest speed command is being 
transmitted into the first loop of the approach section. This restricted 
or stop speed limit must be no higher than that which will allow the train 
to automatically halt within the preselected length of the offset portion 
which is equal to the length of the second loop. This wayside system thus 
controls the cab signal, speed control apparatus on the trains traversing 
the track stretch in a manner disclosed in the previously cited 
application Ser. No. 719,336. A similar wayside operation is provided at 
the end locations where the train enters or exits the single track 
stretch. The directional frequency, however, is not passed by the repeater 
units at these locations, such repeaters being tuned to pass only train 
performance level signals. At each end location, both directional filters 
are connected to the same first loop, that is, of the first section into 
the single track stretch. In other words, there is no directional signal 
in the first loop of the interlocking or station section although speed 
commands are still transmitted through this section from the exit end in 
accordance with the established traffic direction in the advance stretch 
of single track.

In each of the drawings, similar reference characters designate the same or 
similar parts or features of the apparatus. At each location along the 
wayside, a source of direct current energy for operating relays and other 
apparatus is provided. Several types of direct current sources are known 
and used in such signaling systems and therefore the specific source is 
not illustrated. However, the positive and negative terminals thereof and 
connections to them are designated by the reference characters B and N, 
respectively. The source of alternating current energy provided at each 
location for the track circuits and for the track repeater channels is 
illustrated by a conventional symbol such as, for example, the symbol 
designated as 1FT in FIG. 1A. These alternating current sources will 
normally be the commercial source of alternating current energy. Where it 
is necessary, in order to simplify the drawing layout, to illustrate relay 
contacts other than in vertical alignment with the operating winding, such 
contacts are designated by repeating the reference character for the relay 
and distinguishing that contact by a unique lower case letter. An example 
is the contact b of relay 2RH, shown at the lower left of FIG. 1A separate 
from the symbol for that relay operating winding. It is to be noted that 
contacts shown away from the operating winding may also be on a different 
drawing figure from that in which the operating winding is actually 
illustrated. The movable armature of all relay contacts, wherever shown, 
moves up to close against from contacts when the relay winding is 
energized. 
DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
In describing my invention in detail, I shall refer first to FIGS. 1A, 1B, 
and 1C which, taken together in that order with FIG. 1A to the left, show 
a portion of a stretch of railroad track provided with a wayside signaling 
arrangement for controlling cab signals and speed control apparatus on 
trains traversing the track. Under special consideration, FIG. 1A may also 
be placed at the right of FIG. 1C to provide for another end location in 
the stretch of track. Portions of the stretch of track are shown across 
the top of the three drawing figures by the solid lines 11 and 12, each of 
which represent, in a conventional manner, one rail of the track. When 
these lines 11 and 12 are placed in alignment, the wire loop pattern for 
the transmission of cab signal commands will also be completed. Trains 
move in either direction through the stretch of track with the direction 
from left to right being considered as eastbound and the opposite, of 
course, westbound. The portion of track shown is divided into track 
sections by the insulted joints J in rail 11, with sections 1T, 2T, 3T, 
and 4T being shown from left to right. Section 2T is an interlocking or 
station section at which wayside signals 2RG and 2LG control the movement 
of trains into the interlocking and into the following stretch of single 
track. In other words, within section 2T, there may be a station platform 
and also various switches and diverging tracks by which trains may be 
routed to other tracks or routes. For purposes of the description, signal 
2RG is considered to govern train movements in an eastbound direction from 
section 1T through the following or advance sections 2T, 3T, and 4T and 
thence to the right. Signal 2LG governs the movement of westbound trains 
into section 2T and thence through section 1T and subsequent sections in 
that direction. The wayside signals are shown by conventional symbols and 
their specific controls are not shown as they do not form a part of the 
present invention. 
Track circuits are used to detect train occupancy of the various track 
sections shown. Since insulated joints appear only in rail 11, the 
so-called single rail track circuits are specifically used. This is 
conventional and frequency used where the trains are electrically 
propelled. As a specific example, the track circuit for section 3T, which 
laps FIGS. 1B and 1C, is supplied with a source of energy 3FT, shown in 
FIG. 1C by a conventional symbol as an alternating current source. This is 
considered to be the commercial frequency source so that there will be no 
interference with any of the other frequencies used in the speed control 
system. Source 3FT is coupled to rails 11 and 12 of section 3T by the 
track transformer 3TT. At the other end of section 3T, track relay 3TR is 
connected directly across the track rails and is, of course, normally 
energized when no train is occupying this track section. So that the track 
section occupancy condition can be registered at each end of the section, 
a track circuit repeater arrangement is provided. At the west end of 
section 3T, a source of alternating current energy 3FTP, normally the 
commercial source, is connected across the first or principal wire loop 13 
of section 3T by front contacts a and b of relay 3TR. At the other end of 
section 3T, the track repeater relay 3TRP is coupled across the loop by 
the loop transformer 3LT. Obviously, when section 3T is unoccupied, 
repeater relay 3TRP is energized because rack relay 3TR is energized and 
both relays remain in their picked up position to register the 
nonoccupancy of the section. Conversely, a train shunt within the section 
causes both relays to release to register the occupied condition. Similar 
track circuits are provided for each other track section with that for 
section 2T being shown in its entirety while only a partial showing is 
provided for sections 1T and 4T. If FIG. 1A is placed to the right of FIG. 
1C, the track circuit portions for sections 4T and 1T may be combined as 
an illustration of the complete track circuit arrangement for an eastern 
end section of a stretch of railroad track between interlocking or station 
locations. 
Each section is also provided with wire loops to provide channels for the 
transmission of cab signal or speed commands. For example, section 3T has 
a main or first loop 13 which is a two wire closed loop located generally 
along the track center line or midpoint and parallel to the rails. This 
loop begins at the transmitter unit at one end and terminates in the 
receiver unit at the other end, in accordance with the traffic direction, 
as will be described later in the specification. Loop 13 is provided at 
each end of the section with an offset portion of a preselected length and 
positioned immediately adjacent the right-hand rail for trains exiting the 
section at that end. These offset portions are designated 13A for 
eastbound trains and 13B for westbound. This preselected length is equal 
to the stopping distance for a train moving through the section at the 
lowest speed limit. This lowest speed limit is herein designated the STOP 
speed and is defined as a crawling or restricted speed level of 5 mph or 
less. Parallel to the offset portion of the first loop and of the same 
preselected length, a second or auxiliary loop is laid along the track 
center line at each end of the section, the loops 16 and 17. Each of these 
is a closed circuit loop energized from a transmitting unit at the same 
location when that end of the section is the exit for a traffic route. The 
pattern of these loops is similar, as previously mentioned, to that 
described in copending application Ser. No. 719,336 and the same reference 
characters are used in order to provide an easy comparison for this 
section 3T. A similar loop pattern is provided for each other section 
including section 2T, the station or interlocking track section. The 
reference numerals used for the loops in sections 2T and 4T are also the 
same as those used in the cited copending application. Although not shown 
herein, the train carried apparatus which responds to signal commands 
carried in these loops may be the same as that shown in FIG. 2 of the 
cited copending application and reference is made thereto for a 
description of the operation of the train carried cab signal, speed 
control apparatus since this apparatus is not a specific part of the 
invention defined herein. 
I refer now to FIG. 1C in which is illustrated a typical intermediate 
wayside location at a junction between two adjoining track sections, here 
sections 3T and 4T. This location includes apparatus for detecting trains 
or registering the occupancy of both track sections and for the reception 
and transmission of loop signal commands in accordance with the 
established traffic direction and the advance traffic conditions. The 
overall track circuit apparatus has already been described. Here relays 
3TRP and 4TR register the occupancy of sections 3T and 4T, respectively, 
by trains. The loop arrangement for each section has also been previously 
described. Shown at the FIG. 1C location are the first loops 13 and 14 
with their offset portions 13A and 14B, respectively, and second loops 16 
and 19. Coupled to the first loops 14 and 13 are the directional filter 
units 23 and 24, respectively, and connected between these loops is a 
repeater unit 29. Each directional filter unit is tuned to one or the 
other of the distinct directional frequencies FE and FW. For example, 
filter 23 is tuned to respond only to the frequency FE which is 
transmitted to establish the eastbound traffic direction. When this 
frequency is present in the first loops, filter 23 responds to output an 
enabling signal for various coupling units and other elements in a manner 
to be shortly described. These filter units are shown by conventional 
block since any known solid state circuitry which will provide the 
operation desired may be used and the specific details are not part of my 
present invention. 
It is to be noted that these filters will respond to no other signal than 
that to which they are tuned and each is coupled to the loop over which 
the directional signal will be received by repeater unit 29. For example, 
FE filter 23 is coupled to loop 13 by repeater unit 29. In this manner, 
the reception of a directional signal by a filter unit also checks that 
the associated repeater unit is in operable condition. This repeater unit 
29 is provided with filter elements which will pass only frequencies FE 
and FW and other distinct frequencies used as performance level signals in 
the system. Repeater 29 retransmits such signals at a high level through 
the next loop in order to assure the transmission of such signals from one 
end to the other of the stretch. Unit 29 is also shown by a conventional 
block since any known circuitry may be used which will provide the 
operation desired. The so-called performance level commands or signals are 
those which may be used to control the transmission of wayside speed 
commands at a lower level than justified by traffic conditions in order to 
adjust train schedules or the headway between successive trains. Such 
signals may also be received by the train apparatus to establish a 
temporary maximum speed limit lower than the allowable speed or to direct 
the train to bypass a station stop. This performance level signal 
transmission arrangement is not specifically shown herein since the use of 
such signals, particularly transmitted through the rails, is conventional 
and not part of my invention. It will be noted that the repeater units at 
the home signal locations, i. e., each end of the interlocking section 2T, 
are tuned to pass only the performance level (P.L.) commands and not the 
directional frequency signals. 
Each intermediate location also has a receiver and a transmitter unit, such 
as receiver 30 and transmitter 31 in FIG. 1C, for receiving the speed 
commands and for transmitting, through the approach section loops new 
speed commands in accordance with the traffic conditions. The transmitter 
has associated therewith a bank of code generators and a cab signal 
oscillator. This latter unit, in FIG. 1C, is shown as a conventional block 
since any known oscillator circuit may be used which will provide a 
carrier frequency for the transmission of the speed commands, normally in 
the audio frequency range but at a higher frequency if desired or 
required. Code generators, shown by conventional symbols within the 
dot-dash rectangle 32, each generate a specific or distinct signal 
command, for example, in a range from 5 to 22 Hz, which represents a 
specific speed level. The speed ranges are here designated as the maximum 
(MAX), medium (MED), minimum (MIN), and STOP speed levels. The MAX speed 
command allows train movement at whatever maximum speed for the 
transportation system is established. The medium speed level will, for 
example, be on the order of 30 to 35 mph, while a minimum speed level 
will require the train to reduce to a speed of no more than 15 to 20 mph. 
The STOP speed command requires or authorizes a train to move only at a 
crawling speed of 5 mph or less so that it may stop within a very short 
distance, e.g., the offset loop preselected length. The SPECIAL command 
signal is interpreted by the train carried apparatus as the equivalent of 
a MAX speed command. It is used under special wayside conditions to allow 
a clearing out or resetting of an established traffic direction. The code 
commands and the cab signal frequency are both applied to the transmitter 
unit where the command signals modulate the cab signal carrier frequency. 
The modulated carrier is then amplified and transmitted by the transmitter 
unit through the selected wayside loops. Various circuit arrangements for 
generating the code speed command signals are known in the railway 
signaling art. Thus these code generating units are shown in a 
conventional manner since the specific details are not part of the present 
invention and the use of such will be understood by those skilled in the 
art. 
Each receiver unit is tuned to respond only to the cab signal frequency 
and, when enabled by a signal from the active directional filter, is 
operable to demodulate the cab signal carrier and produce a coded output 
signal representing the code or speed command frequency modulated onto the 
cab signal carrier at the transmitter. The output from the receiver is 
applied to a bank of code filters, one for each code rate. Each of these 
filters, shown by a conventional block, is tuned to pass only the assigned 
code rate frequency as designated by the symbol inside the conventional 
block. The output of each code filter is applied to actuate one of the 
associated code generators in a manner in which will be shortly described. 
Each of the code filters is normally a simple filtering circuit tuned to 
pass only the assigned code rate but may, under special conditions as 
specifically shown in FIG. 1C, require an enabling signal to be operable 
to pass the assigned frequency. 
The transmitter and receiver units at each location are coupled to the 
track loops by coupling units such as 25 to 28 shown in FIG. 1C. These 
coupling units, shown conventionally by blocks, are basically known gating 
devices which require an external enabling signal to become conductive. 
These enabling signals are selectively supplied by the directional filters 
FE and FW to alternate pairs of the coupling units. Referring to FIG. 1C, 
when the eastbound traffic direction is established, the coupling units 25 
and 26 are enabled by the FE filter 23 by application of the output of 
this unit to the coupling unit enabling gates. When coupling unit 25 is 
enabled, that is, the circuit is closed, transmitter 31 is connected to 
loop 13 of approach section 3T and also to the second loop 16 of that same 
track section. The connections from the transmitter to loop 16 also 
include front contact c of relay 4TR. Receiver 30 is likewise connected, 
when gate 26 is enabled, to first loop 14 of advance section 4T. It will 
be noted that second loop 19 of advance section 4T is deactivated at this 
time but this is immaterial, in accordance with the operation of the train 
apparatus, since the offset portion 14B will provide signals to an 
eastbound train. When westbound traffic direction is established, coupling 
units 28 and 27 are enabled by the output from FW filter 24 so that 
transmitter 31 is connected to loops 19 and 14 of approach section 4T and 
receiver 30 is connected to loop 13 of advance section 3T. It is to be 
noted that the output from FE filter 23 is also applied over front contact 
d of relay 4TR to enable receiver 30 during eastbound traffic conditions 
while the output of FW filter 24 is applied over front contact b of relay 
3TRP to enable receiver 30 when westbound traffic exists. 
If section 4T is occupied by an eastbound train, relay 4TR is of course 
released. The open front contact d of relay 4TR then interrupts the supply 
of the enabling signal from FE filter 23 to receiver 30 so that, even 
though coupling unit 26 is enabled, receiver 30 is not responsive to the 
signal received from loop 14 through coupling unit 26. However, the 
enabling signal from filter 23 is applied over contact d of relay 4TR to 
the STOP code generator, activating this element to supply its unique code 
rate frequency to transmitter 31. This actuates the transmission of a STOP 
code modulated on the cab signal frequency over loop 13 of section 3T 
since coupling unit 25 is also enabled at this time. However, the open 
front contact c of relay 4TR interrupts transmission of this STOP signal 
to loop 16 so that this loop is deactivated or deenergized under these 
conditions. As previously indicated, a second eastbound train approaching 
through section 3T at the very slow STOP speed will respond to the 
deenergized condition of loop 16 to halt within the preselected length of 
this second loop. 
In a similar manner, if westbound traffic is established and section 3T 
occupied, relay 3TRP releases since relay 3TR at the exist end of section 
3T is also released. Front contact b of 3TRP is thus open, interrupting 
the supply of an enabling signal from FW filter 24 to receiver 30 but the 
corresponding back contact b is closed to apply this signal to the STOP 
code generator of bank 32. Receiver 30 is thus non-responsive to any 
signal received from loop 13 through coupling unit 28, which is enabled, 
but transmitter 31, through coupling unit 27, supplies the cab signal 
carrier modulated by the STOP code signal to loop 14 of section 4T. 
However, front contact a of relay 3TRP is open to interrupt the supply of 
this particular code rate to loop 19 of section 4T. As previously 
described, when auxiliary loop 19 has no signal flowing therein, a 
westbound train approaching at the STOP speed will halt within the length 
of this second loop, short of entering the next track section 3T. 
The apparatus at each end of the interlocking track section 2T is similar 
to that at the intermediate locations. For example, each location at the 
end of section 2T includes a receiver and a transmitter unit with the 
associated code filters and code generators. The transmitter and receiver 
are coupled to the various track loops through gating type coupling units 
as at the intermediate locations. Each such location has a directional 
filter for each direction of traffic and a repeater unit which incidently 
passes only the performance level signal frequency. However, the 
directional filter units at each location in FIGS. 1A and 1B are connected 
to the main loop in the first track section outside of the interlocking 
zone. For example, in FIG. 1B, the FE and FW filter units are each 
connected to loop 13 in section 3T. Correspondingly, in FIG. 1A these 
directional filters are connected to loop 21 in section 1T. In addition, 
the directional filter terminating the traffic direction into the 
interlocking also controls a directional relay with its output or enabling 
signal. For example, the FW filter at the east end of section 2T (FIG. 1B) 
energizes a directional relay 3FWR when the westbound frequency is 
received. When relay 3FWR is energized and picks up, it registers the 
establishment of a westbound traffic direction through the stretch of 
track terminating at the west end of section 3T. In other words, relay 
3FWR registers when a train movement westbound through the stretch and 
entering section 2T at the location of signal 2LG is permitted. Although 
not specifically shown, when the registry of westbound traffic is 
established, that is, relay 3FWR is picked up, it inhibits the clearing of 
the eastbound signal 2RG (FIG. 1A). In a similar manner, the corresponding 
eastbound traffic direction relay 1FER (FIG. 1A) at the other end of the 
interlocking, when energized by the corresponding FE filter, picks up to 
inhibit the clearing of westbound signal 2LG. Each directional relay also 
inhibits, as will be explained, the establishment of the opposite 
direction traffic by preventing the generation of the opposite direction 
traffic frequency. 
A directional frequency oscillator is provided at each interlocking 
location. For example, in FIG. 1A, the FW oscillator provides a signal of 
that frequency while in FIG. 1B, the FE oscillator provides a signal of 
the eastbound frequency. Each of these oscillators is thus the source of 
the directional signal for establishing the traffic for trains leaving the 
interlocking at that particular location. Each oscillator is shown by a 
conventional block since any known type of oscillator which will generate 
or produce a signal of the desired frequency and energy level may be used. 
In FIG. 1B, the FE oscillator is directly connected to loop 13 for 
transmitting a signal through that loop to establish eastbound traffic 
when the oscillator is activated. This oscillator is energized or 
activated when a contact 3ESR is closed in order to selectively establish 
eastbound traffic through the stretch of track beginning at section 3T. 
This energizing circuit also checks that the reception of the 
corresponding westbound frequency has not been registered at that location 
by including back contact a of relay 3FWR. The energizing circuit also 
includes back contact b of an eastbound stretch clear registry relay 
3EDODR which picks up to turn off the FE oscillator when the circuit 
arrangement is clearing out after the passage of an eastbound train and 
the traffic direction is being cancelled. 
The FW oscillator at the other end of the interlocking section 2T is 
controlled in a similar manner, the energizing circuit including back 
contact a of relay 1FER, to assure that the corresponding eastbound 
frequency has not been registered, back contact a of a relay 1WDODR, which 
opens when the stretch has been cleared by a westbound train, and a 
contact 1WSR which is closed when the establishment of westbound traffic 
through the stretch beginning with section 1T is desired. The FW 
oscillator is connected to loop 21 of section 1T to transmit the westbound 
frequency throughout the stretch. It may be noted that an equivalent 
arrangement to that shown in FIG. 1A is provided to the right of FIG. 1C 
at the eastern end of the stretch of track including sections 3T and 4T. 
At each end of the interlocking location, that is, at each end of section 
2T, signal relays responsive to the position or condition of the signals 
2RG and 2LG, governing entry into the interlocking, control the 
application of the STOP speed command to the first loop of the approach 
track section to the interlocking and the interruption of the transmission 
of any signal command in the second loop of the corresponding section. For 
example, when westbound signal 2LG shown in FIG. 1B is displaying a STOP 
indication, the associated signal relay 2LH is released. The illustrated 
front contact a of relay 2LH interrupts the application of speed command 
signals to loop 17 in section 3T which is appropriate since any 
approaching train in this section must stop before it passes the signal. 
Over back contact b of relay 2LH, the enable signal from the FW filter is 
applied to the STOP command generator so that the signal transmitted in 
loop 13 by the transmitter carries the STOP or restricted speed command to 
an approaching train in section 3T. Thus the speed command supplied to 
westbound trains approaching in section 3T directly depends, at least in 
part, upon the condition of signal 2LG and not upon the occupancy of 
section 2T as reflected by relay 2TR. Of course, the clearing of signal 
2LG is dependent upon the non-occupancy of all track sections immediately 
in advance of the signal. Loops 15 and 18 in section 2T, however, are 
controlled in the usual manner for transmitting speed commands to 
eastbound trains approaching through section 2T, whose continued progress 
is dependent upon the occupancy condition of section 3T. 
In FIG. 1A, relay 2RH responds to the condition of the eastbound signal 
2RG. When this signal displays STOP, front contact a of relay 2RH 
interrupts the transmission of speed commands into loop 22 while back 
contact b of this relay transfers the enabling signal from the FE filter 
to the STOP code generator in the code generator bank. Thus the 
transmitter modulates the STOP command onto the cab signal carrier which 
is transmitted into loop 21 to control the approach of the eastbound 
trains. When signal 2RG is in a proceed position, so that relay 2RH is 
picked up, the speed command transmitted into loop 21 and also into loop 
22 depends upon the speed command received through loop 15 in section 2T 
which in turn depends, in the usual manner, upon traffic conditions in 
section 3T and beyond. 
Before briefly describing the operation of the illustrated system, I shall 
refer to FIG. 2. The same stretch of railroad track is shown in each of 
the charts A to E of this drawing figure by a single line symbol. This 
stretch of track is divided by insulated joints, conventionally shown, 
into a plurality of track sections designated across the top of the 
drawing as sections 1T through 8T. Since the charts are vertically aligned 
these section designations apply to each stretch of track illustrated. 
Sections 1T through 4T correspond the section illustrated at least in part 
in FIGS. 1A, B, and C. Sections 5T to 8T of FIG. 2 extend to the right or 
east and have the same or similar wayside apparatus. Section 2T is of 
course the interlocking or station control section with signals 2RG and 
2LG as shown in the various portions of FIG. 1. For controlling each 
direction of train movement, section 8T is a similar interlocking section 
at the east end of the stretch and includes signals 8RG and 8LG for 
governing eastbound and westbound movements, respectively. In using the 
charts of FIG. 2, it is to be noted that the apparatus shown in FIG. 1A 
may also be used to represent the wayside apparatus at the junction of 
sections 7T and 8T. Each of the five charts illustrates a different 
condition of speed command signal transmission in the track loops in 
accordance with the different traffic occupancy conditions. The arrow 
associated with each track section designates the signal flow and the 
associated reference designates the type of command being transmitted. For 
example, in chart A, with no traffic direction established, no speed 
command signals are being transmitted in any section, as designated by the 
zero (0) symbol associated with each arrow. In chart B, a MAX speed code 
command is being transmitted through section 2T from the east end of the 
section in accordance with the apparatus shown in FIG. 1B. 
Chart A of FIG. 2 illustrates the at-rest condition of the apparatus for 
the stretch of track. In other words, neither traffic direction is 
established and no train occupies any of the track sections. Under this 
situation, no cab signal or speed commands are transmitted into any 
section in any direction. By reference to FIGS. 1A and B, it will be seen 
that the FE and FW oscillators are inactive since the ESR and WSR contacts 
are open, no request having been made for the establishment of a traffic 
direction. With no frequency FE or FW signal being transmitted, direction 
filters at each location are inactive and thus produce no enable signal. 
Lacking such an enabling signal, the coupling units or gating circuits are 
not closed to couple the associated transmitters and receivers to the 
track loops. Thus no speed command can be transmitted nor can any signal 
be received from the loops by the local apparatus at any wayside location. 
It is now assumed that an eastbound train is to move through this stretch 
of track from section 2T to section 8T. The dispatcher or control operator 
handling this stretch of track initiates the clearing of signal 2RG and/or 
the establishment of the eastbound traffic direction through the stretch. 
This may be a combined action in accordance with the traffic control 
system in use. In any event, contact 3ESR, shown in FIG. 1B, is closed in 
response to the request for the train movement. The directional signal 
frequency FE is transmitted to loop 13 but is blocked by the P.L. repeater 
unit from being transmitted into loop 15 of section 2T. At the next 
wayside location, FIG. 1C, this eastbound or FE directional signal is 
retransmitted by repeater unit 29 into loop 14. Directional signal FE is 
similarly repeated at each intermediate wayside location and eventually 
received at the east end of section 7T. For example, referring to the 
arrangement for sections 1T and 2T in FIG. 1A as being the equivalent to 
that of sections 7T and 8T, the FE filter is then activated and enables 
the coupling units to connect the receiver to the first loop 15 of section 
8T and the transmitter to the first loop 21 of section 7T. With signal 8RG 
not cleared, a STOP command is transmitted into loop 21 of section 7T and 
the connections to second loop 22 are interrupted so that this loop 
remains deenergized. This action is controlled by a signal relay 8RH and 
its contacts a and b in a manner similar to that described for relay 2RH. 
With reference to FIG. 1C, the reception of the STOP command by the 
receiver unit at the first location to the west of the interlocking, that 
is, at the west end of section 7T where it adjoins section 6T, actuates 
the STOP code filter. This in turn enables the MIN code generator to 
produce a code signal which the transmitter modulates onto the cab signal 
oscillator output. Since eastbound traffic direction is in effect, 
coupling units such as 25 and 26 in FIG. 1C are enabled so that the output 
of the transmitter is connected to the first and second loops of section 
6T to transmit the MIN speed command eastward through this section. At the 
next junction location between sections 6T and 5T, reception of the MIN 
speed command activates the MIN code filter which in turn causes the MED 
code generator to produce a signal which, modulated onto the cab signal 
carrier, is then transmitted in the first and second loops eastward 
through section 5T. At the junction location between sections 4T and 5T, 
reception of the MED speed command causes the code filters to produce a 
signal which actuates the code generators to produce a MAX code signal 
which is transmitted in the first and second loops of section 4T. 
At the junction between sections 3T and 4T, which is specifically shown in 
FIG. 1C, the MAX speed command is received by receiver 30 which is coupled 
by unit 26 to loop 14. With the enabling signal being applied from filter 
23 to the lower of the two MAX code filters shown, the output of this 
filter, as the result of the received code, actuates the SPECIAL code 
generator. This code command is modulated onto the cab signal carrier and 
transmitted eastward in loops 13 and 16 of section 3T. It is to be noted 
that, at the previously described junction locations between the track 
sections, reception of a MAX speed command can activate only the single 
MAX code filter provided, for example, as shown in FIG. 1B. This in turn 
causes the associated MAX code generator to be activated and transmit a 
similar speed command into the eastbound track section loops. However, at 
the junction location in FIG. 1C, it is necessary to provide a SPECIAL 
code command to distinguish between the traffic directions and to actuate 
certain responsive actions at the interlocking location. 
With the FE filter at the section 2T-3T junction (FIG. 1B) activated, the 
associated eastbound coupling units are enabled as is the receiver unit 
since front contact d of relay 3TR is closed. Reception of the SPECIAL 
code command at the location shown in FIG. 1B causes the SPECIAL code 
filter to produce an output. Since the clearing of signal 2RG has been 
requested, relay 2RH is picked up and its front contact c applies this 
output to the MAX code generator so that the transmitter, being connected 
to loops 15 and 18, supplies a MAX speed command in the loops of section 
2T. At the other end of section 2T, shown in FIG. 1A, the eastbound 
direction signal received through loop 21 of section 1T activates the FE 
filter which in turn provides a signal to enable the receiver unit over 
front contact b or relay 2RH. The MAX speed command received through loop 
15 by the receiver is supplied to the code filters, activating the MAX 
filter which in turn applies its output to the MAX code generator for 
further application of this code rate signal to the transmitter. 
Accordingly, a MAX speed command is transmitted via the transmitter 
through loops 21 and 22 of section 1T. This replaces the STOP speed 
command in loop 21 previously transmitted prior to the clearing of the 
eastbound signal 2RG. Reception of this speed command at the west end of 
section 2T also allows signal 2RG to now clear to permit the eastbound 
train movement to pass into section 2T and thus into the stretch of track 
in the eastward direction. It may be noted that, had signal 2RG clear not 
been requested, relay 2RH would be released and, upon the reception of a 
SPECIAL code command at the location in FIG. 1B, the output of the SPECIAL 
code filter would be applied over back contact c of relay 2RH to energize 
relay 3EDODR. 
When the eastbound train accepts the proceed indication on signal 2RG and 
enters section 2T, the signal is returned to its stop indication and the 
clear request is cancelled. This operation is conventional so that the 
signal does not automatically reclear for a following train. Relay 2TR 
releases due to the shunt on the rails of section 2T and in turn 
deenergizes relay 2TRP shown in FIG. 1B. Relay 2RH is also deenergized but 
is provided with slow release characteristics in order not to interrupt, 
at its front contact c in FIG. 1B, the transmission of a MAX speed command 
into loops 15 and 18 of section 2T while the train traverses that section. 
It may be noted that, under most conditions, this interlocking or station 
section 2T will be of considerably shorter length than the intermediate 
sections such as 3T and 4T. When this train enters section 3T, track relay 
3TR releases and in turn deenergizes relay 3TRP which also releases. The 
opening of front contact d of relay 3TR removes the enabling signal from 
the receiver unit which is thus deactivated. Meanwhile, the closing of 
back contact d of relay 3TR supplies the enabling signal to the STOP code 
generator and this speed command is now transmitted into loop 15. However, 
with front contact c of relay 3TR also open, loop 18 is interrupted and 
thus deenergized. 
As the train continues through section 3T and enters section 4T, track 
relay 4TR obviously releases. The shifting of contact d of this relay from 
its front to back position removes the enabling signal from receiver unit 
30 and applies the same signal to activate the STOP code generator. The 
STOP speed command is now transmitted into loop 13 of section 3T by 
transmitter 31 but the connection to loop 16 is interrupted at the open 
front contact c of relay 4TR. Similar actions occur as the train enters 
each new track section as it progresses in the eastward direction. Chart C 
of FIG. 2 illustrates the speed command transmission condition when this 
train is occupying section 7T. 
In considering the operations at the various junction locations when the 
condition of chart C exists, reference is made to the arrangement shown in 
FIG. 1C as being typical of each intermediate location. With section 7T 
occupied, a STOP speed command is then transmitted in the first loop of 
section 6T. However, the second loop of section 6T is deenergized by the 
fact that relay 7TR is released. Thus a following train moving through 
section 6T will be necessity advance at a STOP or restricted speed so that 
it will stop over the second loop due to the absence of any loop signal. 
Since section 6T is unoccupied, its track relay 6TR will be picked up so 
that the receiver unit at the junction between sections 5T and 6T is 
enabled by the FE filter output. The STOP command received through the 
first loop of section 6T and applied to the receiver unit is passed by the 
associated code filters, specifically the STOP code filter, to actuate the 
MIN generator associated with the corresponding transmitter. Thus a MIN 
speed command is transmitted into both loops of section 5T. At the next 
section junction to the west, where sections 4T and 5T are adjoining, the 
MIN speed command received by the receiver unit is passed by the MIN code 
filter to actuate the MED code generator. This results in the MED speed 
command being transmitted through section 4T as indicated in chart C of 
FIG. 2. At the junction between sections 3T and 4T, the MED speed command 
received results in the transmission through loops 13 and 16 of section 3T 
of a MAX speed command. At the interlocking exit, i.e., the junction 
between sections 2T and 3T, reception of the MAX speed command actuates 
the MAX code generator and both loops 15 and 18 in section 2T receive the 
MAX speed command signal. 
When the train moves into section 8T and clears section 7T, signal 8RG 
having previously been cleared, the conditions shown in chart D of FIG. 2 
pertain. Transmission of the various speed commands moves one section to 
the east from that shown in chart C. Even if the dispatcher stores a 
control to reclear signal 8RG, relay 8RH will remain released at the 
present to activate the STOP code generator which results in the 
transmission of such a speed command to the first loop of section 7T. 
Referring now to FIG. 1C, that is, the actual junction between sections 3T 
and 4T, the MAX speed code command received through loop 14 is applied to 
receiver 30. With the FE filter 23 active, this receiver unit together 
with the eastward coupling units are enabled. Similarly, the lower MAX 
code filter element shown in the bank below receiver 30 is likewise 
enabled. Since there is no output from the corresponding FW filter 24, the 
upper MAX code filter is inactive at this time. Thus the only output from 
the code filters is from the lower MAX unit which is then applied to the 
SPECIAL code generator in bank 32. This code rate is applied to 
transmitter 31 and, modulated onto the carrier, then through coupling unit 
25 to loops 13 and 16 of section 3T. 
At the interlocking location shown in FIG. 1B, if signal 2RG is not now 
cleared, the SPECIAL code filter output, over back contact c of relay 2RH, 
energizes relay 3EDODR. Pick up of relay 3EDODR to open its back contact b 
interrupts the circuit energizing the FE oscillator at this location, 
which then ceases to apply the FE directional signal to loop 13. The 
absence of this directional signal causes the apparatus throughout the 
whole stretch to clear out, canceling the eastbound direction previously 
established. This results in renewal of the at-rest condition of the 
apparatus as shown in chart E even though this train has not yet cleared 
section 8T at the east end of the stretch. The operation of the apparatus 
for a westbound train, including the establishment of westbound traffic 
direction, is quite similar and will be obvious by reference to the 
preceding description and to the accompanying drawings. Therefore a 
specific description is omitted. 
The apparatus of my invention thus provides a wayside control arrangement 
for train carried cab signal or speed control apparatus using wire loops 
along the track to transmit cab signal or speed commands for pickup by the 
train receivers. This avoids any interference between the propulsion 
current and the transmitted speed commands since they flow in separate 
channels. Speed commands transmittedare selected in accordance with 
advance traffic conditions which are determined by the registered 
occupancy of the advance track section and the character of the speed 
command received over the advance section first loop. Because of the 
offset of the main loop at the exit end of each section and the provision 
of a second loop, a train is automatically halted prior to entry into an 
advance section occupied by a preceding train. The following train thus 
does not overrun the section junction to inadvertently receive the speed 
command signal being transmitted for the first train. Thus a safe and 
reliable speed control system for railroad trains results. 
Although I have herein shown and described but a single arrangement of a 
wayside signaling system for railroad cab signals and speed control 
embodying features of my invention, it is to be understood that various 
changes and modifications may be made therein within the scope of the 
appended claims without departing from the spirit and scope of my 
invention.