Absolute Block
A system of controlling rail traffic, where (under normal operations) only one train is allowed in the Block Section at a time. Proof of a section clear normally involves the observation of the train tail lamp by the Signaller.

Accelerometer
A device that can measure acceleration generated by the movement of an object along an axis.

Access Point
A device that allows wireless devices to connect to a wired network using Wi-Fi.

Automatic Route Setting (ARS)
A system for setting Routes without the action of the Signaller, based upon a stored timetable, train running information, defined priority, selection criteria and operating algorithms.

Automatic Signal
A Signal controlled by the passage of trains. It does not require any action by the Signaller or ARS. Automatic Signals are usually Passable.

Automatic Track Warning System (ATWS)
A system that gives trackside staff audible and/or visible warning of the approach of trains independently of the Signalling System.

Automatic Train Control (ATC)
Used to describe on-board automation that contributes to or replaces the driver’s judgement as to how to control the train. (ATC=ATO+ATP)

Automatic Train Operation (ATO)
A high reliability system that automatically operates the train’s driving controls in accordance with information usually received from the trackside signalling equipment or traffic control system.

Automatic Train Protection (ATP)
A safety system that enforces either compliance with or observation of speed restrictions and/or Signal Aspects by trains.

Automatic Train Regulation (ATR)
A subsystem to ensure that the train service returns to timetabled operation or to regular, fixed headways, following disruption. ATR subsystems adjust the performance of individual trains to maintain schedules. ATR is normally a subsystem of automatic train supervision (ATS).

Automatic Train Supervision (ATS)
A safety within an automatic train control system which monitors the system status and provides the appropriate controls to direct the operation of trains in order to maintain intended traffic patterns and minimize the effect of train delays on the operating schedule.

Automatic Warning System (AWS)
A system that provides audible and visual warnings to the driver on the Approach To Signals, certain Level Crossings and Emergency, Temporary and certain Permanent, Speed Restrictions. A track Inductor based system linked to the aspects of fixed lineside Signals. The track mounted inductors are supplied as standard or extra strength.

Axle Counter
An axle counter is a device on a railway that detects the passing of a train between two points on a track. Track mounted equipment counts the number of axles entering and leaving a Track Section at each extremity. A calculation is performed to determine whether the track section is Occupied or Clear.

Balise
A track mounted spot transmission unit that uses transponder technology. Its function is to transmit/receive messages to/from the train passing overhead.

Berth
A location where a Train Description may be displayed by the Train Describer and which is normally associated with a Signal.

Braking Curve
A graphical representation of the Braking Distance of a train in relation to the Gradient, the braking characteristics and speed of the train.

Braking Distance (Emergency)
The distance in which a train is capable of stopping in an emergency. Dependent upon train speed, train type, braking characteristics, train weight and/or gradient.

Braking Distance (Service)
The distance in which a train is capable of stopping, from a given speed, at such a deceleration for a passenger train that the passengers do not suffer discomfort or alarm, or at an equivalent deceleration in the case of non-passenger trains.

Cab Secure Radio (CSR)
A secure radio communication system between driver and Signaller.

Cab Signal
A display in the driving cab of a train, showing Permissible Speed or extent of Movement Authority, instead of or supplementing lineside Signals.

Call-By
The authority given by a Signaller to a driver to pass a Signal at Danger.

Communications-Based Train Control (CBTC)
A railway signaling system that makes use of the telecommunications between the train and track equipment for the traffic management and infrastructure control. By means of the CBTC systems, the exact position of a train is known more accurately than with the traditional signaling systems.

Computer Based Interlocking (CBI)
A generic term for a second generation processor based system for controlling the Interlocking between Points and Signals, as well as communication with lineside Signalling Functions.

Degraded Mode Conditions
The state of the part of the railway system when it continues to operate in a restricted manner due to the failure of one or more components.

Dispatcher
An employee who supervises the train movements of a line or a certain area. A dispatcher may also perform the duty of a Train Control Operator.

Driverless Train Operation (DTO)
A signal train operation where starting and stopping are automated but a train attendant operates the doors and drives the train in case of emergencies, or GoA3.

Dwell Time 
The total elapsed time from the time that a train stops in a station until the time it resumes moving.

Emergency Release
A device, usually sealed, to permit the operation of a Signalling Function in case of emergency or failure.

European Rail Traffic Management System (ERTMS)
A system for managing rail traffic, enabling it to operate on compatible Signalling Systems across European borders.

European Train Control System (ETCS)
The train control part of ERTMS.

a.       Level -1; An intermittent ATP system following the ETCS standard that uses controlled Eurobalises for transmission of control data.

b.       Level -2; An continuous ATP system following the ETCS standard that that combines radio-based train control with a fixed block system.

c.       Level -3; An continuous ATP system following the ETCS standard that that combines radio-based train control with radio-based train separation based on moving block or virtual block.

Eurobalise
A standardised balise for use in the European Train Control System.

Fail-Safe
A design philosophy which results in expected failures maintaining or placing the equipment in a safe state.

Fixed Block
The section of track between two fixed points.

Flank Protection
Protection from overrunning movements approaching on converging tracks, usually by additional Point Interlocking or Train Detection.

Grades of Automation (GoA)
There are various degrees of automation; these are defined according to which basic functions of train operation are the responsibility of staff, and which are the responsibility of the system itself.

Hazard
Any real or potential condition that can cause injury, death, or damage or loss of equipment or property.

Handsignal
An indication given to the driver of a train during Shunting Movements or in other exceptional circumstances to control the movement of the train.

Headway
The shortest distance or time interval between two following trains, so that the second train can run at its normal operating speed without being restricted by the Signal Aspects.

Interlocking
An electrical, electronic or mechanical means of making the operation of one piece of apparatus dependent upon certain predetermined conditions being fulfilled by other apparatus. The logic by which routes that conflict are prevented from being set at the same time.

Lever
The normal state of a Block Section when no permission has been given for a train to enter it.

Line Blocked (LB)
The normal state of a Block Section when no permission has been given for a train to enter it.

Line Capacity
For a given section of line, the practical maximum number of trains per hour permitted by the Signalling System.

Line Clear (LC)
The state of the Block Section after a train has been accepted but before it has entered the block section.

Line Clear
Release The Signaller can only pull the lever for the Section Signal if Line Clear is obtained from the box ahead. The lever is released either for One Pull or One Train.

Line Speed
Obsolete term for Permissible Speed.

Moving Block
A signalling block system where the blocks are defined in real time by computers as safe zones around each train.

Non-Passable
A Signal is designated Non-Passable because it protects an area of conflict or other infrastructure such that a significant hazard would arise in the event of it being passed at danger without authority. Such Signals cannot be passed at danger without specific authority from the Signaller, in accordance with the Rule Book. Non-passable Signals are usually Controlled Signals.

Non-Safety
Related A description applied to those parts of the Signalling System whose failure or non-availability does not directly endanger rail traffic or reduce the integrity of the Signalling System.

Non-Vital
Signalling equipment and circuits are considered non vital where failure to function correctly would not cause an unsafe outcome of the signalling system. Non-vital equipment and circuits do not affect the safe operation of the signalling system.

Odometer
A device that measures the distance travelled based on wheel revolutions, radar and/or accelerometers.

Operations Control Center (OCC)
A location or locations designed, equipped, and staffed for the purposes of monitoring and controlling rail transit service activities from a central location or locations.

Overlap (OL)
The distance beyond a Stop Signal that must be clear, and where necessary Locked, before the Stop Signal preceding the Stop Signal in question can display a Proceed Aspect.

Point Machine (or Switch Machine)
A machine that is used to operate points, movable frogs or derailers.

Radio Block Centre
A control centre to supervise and control train movements in a territory with radio-based train control.

Safety Integrity Level (SIL)
Defined as a relative level of risk-reduction provided by a safety function, or to specify a target level of risk reduction.

Semi-automatic Train Operation (STO)
A signal train operation where stopping is automated but a driver in the cab starts the train, operates the doors, drives the train if needed and handles emergencies. GoA2

Switch
A track structure of movable running rails (points) with necessary fastening to provide a means for routing trains from one track to another.

Tachometere
An instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine.

Timetable
A document that contains the schedules of all trains of a line.

Track Circuit (TC)
An electrical device using the rails in an electric circuit, which detects the absence of trains on a defined section of line.

Track Section
A portion of railway track having fixed boundaries and for which the Train Detection System provides information on its state of occupancy to the Signalling System.

Train Detection System
Equipment and systems forming part of, or providing input to, the Signalling Systems to detect, either:

a.       the presence or absence of vehicles within the limits of a track section, or

b.       that a train has reached, is passing or has passed a specific position.

Where required, a train detection system may additionally detect the direction in which a train is travelling.

Transponder
A transponder is a wireless communications, monitoring, or control device that picks up and automatically responds to an incoming signal. The term is a contraction of the words transmitter and responder. Transponders can be either passive or active.

Turnout Speed
The speed permitted through the Facing Points when Set for the Diverging Route.

Unattended Train Operation (UTO)
A signal train operation where starting and stopping, operation of doors and handling of emergencies are fully automated without any on-train staff, or GoA4.

Vehicle On-Board Controller (VOBC)
It establishes the position of the train on the guideway by detecting transponders located in the track bed, and uses the transponder data to extract information from the database. Database on the Vehicle On-board Controller contains all relevant guideway information, including station stops, gradients, civil speed limits, switch locations, axle counter blocks locations and trackside signal locations.

Vital
Equipment whose correct operation is essential to the integrity of the Signalling System. Most vital equipment is designed to Fail-Safe principles – a Wrong Side Failure of vital equipment could directly endanger rail traffic.

Vital Function
A function in a safety critical system that is required to be implemented in a fail-safe manner.

Most railroads use track circuits to determine which sections of track are occupied by trains. These devices are actually fairly simple in design, and have been in use since 1872.

In order for the system to work, tracks are divided into blocks of varying length. Each block is divided from the adjacent blocks by an insulated joint between rails. Blocks often have signals at each end to control train movements. Signals are transmitted to the cab of the train, and are not present next to the tracks except at switches. Each block has a track circuit which determines whether a train is present.

Track circuits work by running a circuit using the rails to connect a power source at one end of the block with a relay at the far end. The relay and power source are connected to each rail by cables. As long as the circuit is complete, low voltage power flows down one rail, through a relay, and returns to the power source via the other rail. If the circuit is complete, the relay will be energized, which keeps signals in the “clear” position. If the circuit is broken, the system fails in a safe manner. A broken rail or a failed power source causes the relay to become de-energized and report the section of track as occupied.

Unoccupied Track Circuit; The power source is located at the number “1”, with the relay shown at number “2”. The completed circuit is shown in yellow on the diagram.

Occupied Track Circuit; A train is detected because it shorts the circuit. In railroading, this is called “shunting” the circuit. When a train enters a block, the metal wheels and axle conduct the circuit as a short cut which bypasses the relay. This de-energizes the relay, which causes signals to report the block as occupied. This is reflected in diagram:  “1” shows the power source, “3” is the wheel/axle of a train, and “4” is the de-energized relay.

Metro’s Track Circuit system is a little more advanced. In Metro’s case, each block has a relay on each end called a “Wee-Z bond”. These bonds are split between blocks. Each one acts as a transmitter for one block and a receiver for the adjacent block. If a given block’s transmitter (“5”) and receiver (“6”), located on opposite ends of the block, have a complete circuit, the block is considered unoccupied, and therefore safe for trains to enter.

If, however, a train is in the block, the transmitter/receiver circuit is broken, stopping subsequent trains from entering the block. Speed commands are sent to the train in the block through the transmitter bond. The commands are sent as high-frequency audio waves through the running rails. The ATC computer uses data from the blocks to determine which blocks are occupied, and therefore how to space trains.

In general railroad signals work like traffic signals – they can’t prevent a train from passing a stop signal, they just alert a driver to stop. However, many railroads and transit operators have systems which can stop a train. When red, the arm is in the up position, and it hits a valve on trains that pass it which applies the emergency brake.

Metro’s system uses Automatic Train Control (ATC) to enforce stop commands and keeps trains safely spaced by controlling train speeds. Because signals are not present on the wayside, operators know whether it is clear to proceed through cab signaling. The ATC system sends speed commands to the train and the speed appears on the operator’s console. In both manual and automatic operation, the ATC system automatically applies the brakes if the train’s speed exceeds the regulated speed for more than 2 seconds.

Balise is an electronic beacon or transponder placed between the rails of a railway as part of an automatic train protection (ATP) system. Transmission device (passive transponder) that can send telegrams (or tele-powering) to an on-Board subsystem passing over it. The on-board system tracks the train’s location by counting wheel rotations, and correcting at fixed locations known as balises. Balises constitute an integral part of the European Train Control System, where they serve as “beacons” giving the exact location of a train. A balise which complies with the European Train Control System specification is called a Eurobalise.

Eurobalise is the European system for the transmission of information relevant to safety between the train and the trackside equipment. It’s a function of ERTMS (European Rail Traffic Management System) and one of the sub-systems of ETCS (European Train Control System).

It is used at all ERTMS/ETCS application levels (Level 0, Level 1, Level 2, Level 3 and Level STM).

The Eurobalise system consists of:

a.       Balise: beacons, fixed or controlled type, situated along the railway track, which are energised and enabled to transmit only when the train antenna is above them;

b.       On-board transmission system: consisting of the antenna unit and BTM (Balise Module Transmission) function;

c.       Trackside signalling system: consisting of the LEU (Lineside Electronic Unit) and other external equipment involved in the signalling process.

ERTMS Level 1

ERTMS Level 2

ERTMS Level 3

The system function of balise information transmission system is accomplished by two signal transmission processes, i.e., the tele-powering transmission process where the on-board balise transmission module (BTM) radiates energy waves to activate the ground balise to start to work and the up-link signal transmission process where the ground balise transmits important control information to the train subsequently.

Through the two processes, the ground-train point-mode information transmission is achieved, and the telegram information including geographical position, route data and temporary speed limitis passed to the on-board unit which continuously calculates the dynamic speed profile from these data and other information concerning train performans, thus realizing the real-time supervision of train speed. Therefore, balise information transmission system is very important for train operation safety.

An axle counter is a device on a railway that detects the passing of a train between two points on a track. A counting head (or detection point) is installed at each end of the section, and as each train axle passes the counting head at the start of the section, a counter increments. A detection point comprises two independent sensors, therefore the device can detect the direction and speed of a train by the order and time in which the sensors are passed. As the train passes a similar counting head at the end of the section, the counter compares count at the end of the section with that recorded at the beginning. If the two counts are the same, the section is presumed to be clear for a second train.

This is carried out by safety critical computers called ‘evaluators’ which are centrally located, with the detection points located at the required sites in the field. The detection points are either connected to the evaluator via dedicated copper cable or via a telecommunications transmission system. This allows the detection points to be located significant distances from the evaluator. This is useful when using centralised interlocking equipment but less so when signalling equipment is distributed at the lineside in equipment cabinets.

Components of the system

The main components of the system are:

a.       Outdoor equipment (detection points in the track area)

b.       Information transmission equipment (cables)

c.       Indoor equipment (evaluation, indication & resetting)

Advantages

The advantages of Axle counter that-

a.       It does not require wooden sleepers (where concrete sleepers are not available) except for short track circuits to suppress the counts due to movement of insulated trolleys.

b.       An axle counter system can cover a very long section up to 15 Kms.

c.       It does not get affected either by flooding of track or poor maintenance of tracks unlike the track circuit, which is highly susceptible to these conditions.

d.       It does not require insulating rail joints, thus, rails can be continuously welded. This reduces track maintenance cost, low wear and tear of tracks and vehicles and to increase traveling comfort.

e.       Efficiency and safe working of axle counters does not depend up various track parameters and climate condition such as length, ballast condition, drainage, stray voltage and currents, track feed voltage and lead cables, etc. like track circuits.

Disadvantages

a.       The quality of the electrical signal transmitted by the rail is dependent on the insulation resistance of the ties and the ballast. Causes leakage currents (if insufficient).

b.       This resistance is a limiting factor for the maximum length of the track circuit.

Applications

Axle counters have been finding more and more uses on modern safety signaling systems in railways. These are being used presently for the following.

a.       Monitoring of berthing tracks in station areas and yards.

b.       Monitoring of point zones in station areas and yard.

c.       Automatic Signaling systems.

d.       Block working through axle counters using multiplexers (USBI) with cable, OFC or radio communication (Last Vehicle Checking Device /Axle Counter Block Working/Block Proving by Axle Counter).

e.       Level-crossing warning system using axle counter. (f) Intermediate Block Signaling in Double line sections.

Communications-Based Train Control (CBTC) is a railway signaling system that makes use of the telecommunications between the train and track equipment for the traffic management and infrastructure control. By means of the CBTC systems, the exact position of a train is known more accurately than with the traditional signaling systems. This results in a more efficient and safe way to manage the railway traffic. Metros (and other railway systems) are able to improve headways while maintaining or even improving safety.

A CBTC system is a “continuous, automatic train control system utilizing high-resolution train location determination, independent of track circuits; continuous, high-capacity, bidirectional train-to-wayside data communications; and trainborne and wayside processors capable of implementing Automatic Train Protection (ATP) functions, as well as optional Automatic Train Operation (ATO) and Automatic Train Supervision (ATS) functions.”, as defined in theIEEE 1474 standard.

City and population growth increases the need for mass transit transport and signalling systems need to evolve and adapt to safely meet this increase in demand and traffic capacity. As a result of this operators are now focused on maximising train line capacity. The main objective of CBTC is to increase capacity by safely reducing the time interval (headway) between trains travelling along the line.

Traditional legacy signalling systems are historically based in the detection of the trains in discrete sections of the track called ‘blocks’. Each block is protected by signals that prevent a train entering an occupied block. Since every block is fixed by the infrastructure, these systems are referred to as fixed block systems.

Unlike the traditional fixed block systems, in the modern moving block CBTC systems the protected section for each train is not statically defined by the infrastructure (except for the virtual block technology, with operating appearance of a moving block but still constrained by physical blocks). Besides, the trains themselves are continuously communicating their exact position to the equipment in the track by means of a bi-directional link, either inductive loop or radio communication.

This technology, operating in the 30–60 kHz frequency range to communicate trains and wayside equipment, was widely adopted by the metro operators in spite of someelectromagnetic compatibility (EMC) issues, as well as other installation and maintenance concerns.

As with new application of any technology, some problems arose at the beginning mainly due to compatibility and interoperability aspects.  However, there have been relevant improvements since then, and currently the reliability of the radio-based communication systems has grown significantly.

Moreover, it is important to highlight that not all the systems using radio communication technology are considered to be CBTC systems. So, for clarity and to keep in line with the state-of-the-art solutions for operator’s requirements,  this article only covers the latest moving block principle based (either true moving block or virtual block, so not dependent on track-based detection of the trains) CBTC solutions that make use of the radio communications.

Main features

CBTC and moving block

CBTC systems are modern railway signaling systems that can mainly be used in urban railway lines (either light or heavy) and APMs, although it could also be deployed oncommuter lines. For main lines, a similar system might be the European Railway Traffic Management System ERTMS Level 3 (not yet fully defined). In the modern CBTC systems the trains continuously calculate and communicate their status via radio to the wayside equipment distributed along the line. This status includes, among other parameters, the exact position, speed, travel direction and braking distance. This information allows calculation of the area potentially occupied by the train on the track. It also enables the wayside equipment to define the points on the line that must never be passed by the other trains on the same track. These points are communicated to make the trains automatically and continuously adjust their speed while maintaining the safety and comfort (jerk) requirements. So, the trains continuously receive information regarding the distance to the preceding train and are then able to adjust their safety distance accordingly.

fixed block

moving block

From the signalling system perspective, the first figure shows the total occupancy of the leading train by including the whole blocks which the train is located on. This is due to the fact that it is impossible for the system to know exactly where the train actually is within these blocks. Therefore, the fixed block system only allows the following train to move up to the last unoccupied block’s border.

In a moving block system as shown in the second figure, the train position and its braking curve is continuously calculated by the trains, and then communicated via radio to the wayside equipment. Thus, the wayside equipment is able to establish protected areas, each one called Limit of Movement Authority (LMA), up to the nearest obstacle (in the figure the tail of the train in front).

It is important to mention that the occupancy calculated in these systems must include a safety margin for location uncertainty (in yellow in the figure) added to the length of the train. Both of them form what is usually called ‘Footprint’. This safety margin depends on the accuracy of the odometry system in the train.

CBTC systems based on moving block allows the reduction of the safety distance between two consecutive trains. This distance is varying according to the continuous updates of the train location and speed, maintaining the safety requirements. This results in a reduced headway between consecutive trains and an increased transport capacity.

Levels of automation

Modern CBTC systems allow different levels of automation or Grades of Automation, GoA, as defined and classified in the IEC 62290-1. In fact, CBTC is not a synonym for “driverless” or “automated trains” although it is considered as a basic technology for this purpose.

The grades of automation available range from a manual protected operation, GoA 1 (usually applied as a fallback operation mode) to the fully automated operation, GoA 4 (Unattended Train Operation, UTO). Intermediate operation modes comprise semi-automated GoA 2 (Semi-automated Operation Mode, STO) or driverless GoA 3 (Driverless Train Operation, DTO). The latter operates without a driver in the cabin, but requires an attendant to face degraded modes of operation as well as guide the passengers in the case of emergencies. The higher the GoA, the higher the safety, functionality and performance levels must be.

Main advantages of the Communications-Based Train Control System:

a.       Optimized train speeds to gain best line capacity, reduced costs and provide best passenger comfort;

b.       Guaranteed short term of system delivery and launching;

c.       Putting in operation from day one;

d.       Automated operations and easy maintenance;

e.       Driverless system (or upgradable to driverless) to reduce operating costs;

f.        Power saving;

g.       Easy maintenance;

h.       Easy expansion;

i.        Easy integration;

j.        Best immunity against interference;

k.       Obsolescence-proof;

l.        100% safe;

m.     Minimum trackside equipment.

Innovative solution simplifies the complex route setting and interlocking functions, completely merging them into CBTC:

a.       Optimum train-centric architecture, with more on-board intelligence and direct train-to-train communication, leading to 20% less equipment and better performances;

b.       Higher transport capacity with minimal headway (down to 60 seconds);

c.       Higher operational availability (24 hours) with extreme flexibility of train movements;

d.       Optimal investment and LCC for all types of line configuration.

e.       CBTC can be easily integrated with all automation systems for railway transport.

Architecture

The typical architecture of a modern CBTC system comprises the following main subsystems:

Wayside equipment, which includes the interlocking and the subsystems controlling every zone in the line or network (typically containing the wayside ATP and ATO functionalities). Depending on the suppliers, the architectures may be centralized or distributed. The control of the system is performed from a central command ATS, though local control subsystems may be also included as a fallback.

CBTC onboard equipment, including ATP and ATO subsystems in the vehicles.

Train to wayside communication subsystem, currently based on radio links.

Thus, although a CBTC architecture is always depending on the supplier and its technical approach, the following logical components may be found generally in a typical CBTC architecture:

Onboard ATP system. This subsystem is in charge of the continuous control of the train speed according to the safety profile, and applying the brake if it is necessary. It is also in charge of the communication with the wayside ATP subsystem in order to exchange the information needed for a safe operation (sending speed and braking distance, and receiving the limit of movement authority for a safe operation).

Onboard ATO system. It is responsible for the automatic control of the traction and braking effort in order to keep the train under the threshold established by the ATP subsystem. Its main task is either to facilitate the driver or attendant functions, or even to operate the train in a fully automatic mode while maintaining the traffic regulation targets and passenger comfort. It also allows the selection of different automatic driving strategies to adapt the runtime or even reduce the power consumption.

Wayside ATP system. This subsystem undertakes the management of all the communications with the trains in its area. Additionally, it calculates the limits of movement authority that every train must respect while operating in the mentioned area. This task is therefore critical for the operation safety.

Wayside ATO system. It is in charge of controlling the destination and regulation targets of every train. The wayside ATO functionality provides all the trains in the system with their destination as well as with other data such as the dwell time in the stations. Additionally, it may also perform auxiliary and non-safety related tasks including for instance alarm/event communication and management, or handling skip/hold station commands.

Communication system. The CBTC systems integrate a digital networked radio system by means of antennas or leaky feeder cable for the bi-directional communication between the track equipment and the trains. The 2,4GHz band is commonly used in these systems (same as WiFi), though other alternative frequencies such as 900 MHz (US), 5.8 GHz or other licensed bands may be used as well.

ATS system. The ATS system is commonly integrated within most of the CBTC solutions. Its main task is to act as the interface between the operator and the system, managing the traffic according to the specific regulation criteria. Other tasks may include the event and alarm management as well as acting as the interface with external systems.

Interlocking system. When needed as an independent subsystem (for instance as a fallback system), it will be in charge of the vital control of the trackside objects such as switches or signals, as well as other related functionality. In the case of simpler networks or lines, the functionality of the interlocking may be integrated into the wayside ATP system.