Rail Cybersecurity, Term by Term

ATP

ATP / ATO / ATC

Automatic Train Protection (ATP) enforces speed and movement limits and is safety-critical. Automatic Train Operation (ATO) drives the train: acceleration, braking and station stops. Automatic Train Control (ATC) is the umbrella term combining both with Automatic Train Supervision (ATS).

Axle Counter

An axle counter is a train detection system that counts wheel axles entering and leaving a track section using sensors clamped to the rail. When the number of axles counted out equals the number counted in, the section is clear. It is the main alternative to track circuits in modern signaling.

Balise / Eurobalise

A balise is a passive transponder mounted between the rails that transmits a short data telegram to a passing train. In ETCS, Eurobalises give the onboard unit a precise location reference and, in Level 1, carry movement authority and speed information from the lineside signals to the train.

CBTC

Communications-Based Train Control (CBTC)

Communications-Based Train Control (CBTC) is a railway signaling system that locates each train through continuous radio data exchange between trains and wayside equipment, rather than track circuits. This enables moving-block operation: trains run at shorter, dynamically calculated headways, increasing line capacity. Used mainly in metro and urban rail.

DCS

Data Communication System (DCS)

The Data Communication System is the radio and backbone network that connects trains to the wayside in a CBTC system. It carries the continuous exchange of position reports and movement authorities between onboard controllers and zone controllers that moving-block operation depends on.

ETCS

ETCS / ERTMS

ERTMS (European Rail Traffic Management System) is the EU standard for interoperable railway signaling. ETCS, its train-control component, transmits movement authorities to the onboard unit via trackside balises (Level 1) or GSM-R/FRMCS radio (Levels 2 and 3), continuously supervising speed and braking.

EULYNX

EULYNX is a European railway initiative that standardizes the interfaces (SCI-P, SCI-LS, SCI-LX and others) between interlockings and field elements such as points, signals and level crossings. It replaces proprietary, relay-based connections with IP-based protocols, using RaSTA for safe transport.

EVC

European Vital Computer (EVC)

The European Vital Computer is the safety computer at the heart of the ETCS onboard unit. It receives data from balises and the Radio Block Centre, calculates the train's position and permitted speed, supervises the driver's actions and applies the brakes if the train exceeds its movement authority.

FRMCS

FRMCS

FRMCS, the Future Railway Mobile Communication System, is the 5G-based radio system defined by the UIC to replace GSM-R. It will carry ETCS train control data, voice communication between drivers and controllers, and new applications such as ATO and video, on a bearer-independent architecture designed to outlive any single radio technology.

GoA

Grades of Automation (GoA)

Grades of Automation (GoA) is the IEC 62290 scale for how much of train operation is automated: GoA0 (on-sight), GoA1 (manual with protection), GoA2 (semi-automatic, driver present), GoA3 (driverless with attendant) and GoA4 (unattended). Higher grades shift safety enforcement from the driver to networked control systems.

GSM-R

GSM-R (GSM-Railway) is a rail-specific variant of the GSM mobile standard that provides voice and data communication between trains and trackside, and carries ETCS Level 2 and 3 movement authorities. It is being succeeded by FRMCS, the 5G-based Future Railway Mobile Communication System.

CBI

Interlocking

An interlocking is the signaling apparatus, relay-based or computer-based, that ensures signals, points (switches) and track sections are set in a safe, non-conflicting configuration before a route is cleared for a train. It is the core safety logic that prevents conflicting train movements.

JRU

Juridical Recorder Unit (JRU)

The Juridical Recorder Unit (JRU) is the onboard black box of an ETCS-equipped train. It records driving and train-control data (speed, brake commands, movement authorities and driver actions) as defined in UNISIG Subset-027, for post-incident investigation and audit.

Moving Block

Moving block is a train-separation method in which the protected zone behind each train moves with it, sized in real time from the train's position and braking performance. Unlike fixed-block signaling, it lets trains follow more closely, raising line capacity. It is enabled by CBTC and ETCS Level 3.

OC

Object Controller (OC)

An object controller is a trackside computer that connects field elements such as points, signals, level crossings and train detection to a digital interlocking over an IP network. It translates the interlocking's commands into electrical actions and reports the status of the elements back to the interlocking.

PIS

Passenger Information System (PIS)

A passenger information system delivers announcements, next-stop displays, service updates and advertising to passengers on trains and in stations. Onboard, it typically shares the train's Ethernet network with control and diagnostic systems and connects to the ground through cellular links to receive live content.

PTC

Positive Train Control (PTC)

Positive Train Control (PTC) is a North American mainline safety overlay, mandated by US law, that automatically enforces speed limits and movement authorities to prevent train-to-train collisions, overspeed derailments, work-zone incursions and movement through misaligned switches. It combines GPS, 220 MHz radio and wayside interface units.

RBC

Radio Block Centre (RBC)

A Radio Block Centre is the trackside computer in ETCS Level 2 and Level 3 that issues movement authorities to trains over radio. It takes track occupancy and route status from the interlocking, tracks each train's reported position, and calculates how far and how fast each train may safely travel.

SCADA

Rail SCADA

Rail SCADA refers to the supervisory control and data acquisition systems that operate a railway's non-signaling infrastructure: traction power substations and catenary sectioning, tunnel ventilation, pumps, lighting, escalators and station systems. Operators in a control center monitor and command remote equipment through a network of controllers and remote terminal units.

Track Circuit

A track circuit is an electrical circuit that uses the rails themselves to detect whether a section of track is occupied. A current flows through the rails between a transmitter and a receiver; when a train's wheels and axles short the rails together, the receiver drops out and the section is reported occupied.

TMS

Traffic Management System (TMS) / CTC

A traffic management system is the control-center software that dispatchers use to plan and supervise train movements across a network. It displays the state of the railway, sets routes through interlockings, manages the timetable and resolves conflicts. In North America the equivalent function is known as Centralized Traffic Control.

TCN

Train Communication Network (TCN)

The Train Communication Network is the family of onboard data networks standardised in IEC 61375 that connects the control units, sensors and subsystems of a train. It includes the Ethernet Train Backbone linking vehicles or consists and the Ethernet Consist Network within them, alongside the older MVB and WTB buses.

TCMS

Train Control and Management System (TCMS)

The Train Control and Management System (TCMS) is the onboard control network that coordinates a train's subsystems (traction, braking, doors, HVAC and diagnostics) over train buses such as MVB, WTB or Ethernet (IEC 61375). It is the train's internal industrial network and a central onboard cybersecurity concern.

Wayside

Wayside refers to fixed railway installations along the track, such as interlockings, level crossings, track circuits, points, signals and the networks connecting them, as distinct from rolling stock (onboard) systems. Wayside and onboard are the two deployment domains of rail OT security.

WSM

Wayside Status Message (WSM)

In Positive Train Control, a Wayside Status Message (WSM) is a message broadcast by a wayside interface unit reporting the state of signals and switches to approaching trains. Gaps in WSM reception indicate lost radio coverage or equipment faults and can force trains to slow or stop.

APTA

APTA Cybersecurity Standards

The American Public Transportation Association publishes voluntary cybersecurity standards, frameworks and white papers written specifically for transit agencies, developed by its Transit Cybersecurity Working Group (TCSWG). They cover securing control and communications systems in rail transit and, through the OT Cybersecurity Maturity Framework (OT-CMF), give agencies a structured way to assess and improve the security of their operational technology.

CENELEC EN 50126 / 50128 / 50129

EN 50126, EN 50128 and EN 50129 are the European railway RAMS standards. EN 50126 defines the reliability, availability, maintainability and safety lifecycle; EN 50128 covers software for railway control and protection systems (Safety Integrity Levels); EN 50129 covers safety-related electronic signaling systems.

TS 50701

CLC/TS 50701

CLC/TS 50701 is the CENELEC technical specification, published in 2021, that adapted the IEC 62443 industrial security series to railways. It defines how to apply zones, conduits, security levels and a security lifecycle to signaling, rolling stock and fixed installations. Its content has been carried forward into the international standard IEC 63452.

CRA

EU Cyber Resilience Act (CRA)

The Cyber Resilience Act is the EU regulation that sets mandatory cybersecurity requirements for products with digital elements sold in the European market, from consumer devices to industrial controllers. Manufacturers must build security into their products, handle vulnerabilities throughout the support period and report actively exploited vulnerabilities and serious incidents to the authorities.

IEC 62443

IEC 62443 is the international standard series for securing industrial automation and control systems (IACS). It defines zones and conduits, Security Levels 1 to 4, and requirements for asset owners, integrators and product suppliers. IEC 62443-3-3 sets system-level security requirements and is widely applied to rail.

IEC 63452

IEC 63452 is the international standard for railway cybersecurity, published in 2025, evolving the earlier CENELEC TS 50701. It applies the IEC 62443 approach across the railway lifecycle (risk assessment, zoning, security requirements and operations) for signaling, rolling stock and fixed installations.

NIS2 Directive

The NIS2 Directive (EU 2022/2555) is the European Union's cybersecurity law for essential and important entities. Rail infrastructure managers and railway undertakings fall under the transport sector, with obligations for risk management, incident reporting and management accountability, enforced through national legislation.

NIST

NIST

NIST, the US National Institute of Standards and Technology, publishes the cybersecurity frameworks and guidelines that US transit and rail operators most often build their programs on: the Cybersecurity Framework (CSF), the OT security guide SP 800-82 and the Transit CSF Community Profile (NIST IR 8576) that applies the CSF to transit agencies.

SIL

Safety Integrity Level (SIL)

A Safety Integrity Level is a measure, from SIL 1 to SIL 4, of how reliably a safety function must perform to reduce risk to a tolerable level. In railways it is defined by the CENELEC standards EN 50126, 50128 and 50129, and signaling functions such as interlocking and train protection are typically required to meet SIL 4, the highest level.

SL

Security Level (SL)

A Security Level, in IEC 62443, is a rating from SL 1 to SL 4 that describes how capable an attacker a zone or component must withstand. SL 1 protects against casual or accidental misuse; SL 4 against a well-resourced, highly motivated adversary. Rail standards such as IEC 63452 use the same scale.

SecRAC

Security-Related Application Conditions (SecRAC)

Security-Related Application Conditions are the rules and assumptions a supplier hands over with a product or subsystem that the operator or integrator must satisfy for the delivered security level to hold. Defined in TS 50701 and IEC 63452, they are the cybersecurity counterpart to the Safety-Related Application Conditions of EN 50129.

TSA

TSA Security Directive 1580/82

TSA Security Directives 1580/82 are US Transportation Security Administration directives, first issued in 2022 and renewed annually, for freight and passenger rail owners and operators. They require network segmentation, access control, continuous monitoring and detection, and patch management for critical cyber systems.

Air-Gapped Network

An air-gapped network has no outbound connectivity to the internet or to corporate systems. Air-gapping is common in rail signaling and reduces exposure, but it does not eliminate risk: maintenance laptops, removable media and vendor access remain entry points, and monitoring must work without cloud connectivity.

Anomaly Detection

Anomaly detection is a security technique that learns the normal behaviour of a network or system and raises alerts when activity deviates from it. In OT, where communication patterns are highly repetitive and predictable, it can reveal attacks and misconfigurations that have no known signature.

DPI

Deep Packet Inspection (DPI)

Deep packet inspection is the analysis of network traffic beyond addresses and ports, into the content of the application-layer messages. In rail OT it means decoding signaling, train control and SCADA protocols to understand which commands are being sent, by whom, to which device and with what values.

IDS

Intrusion Detection System (IDS)

An intrusion detection system monitors a network or host for signs of malicious activity or policy violations and alerts security staff. In OT, an IDS is almost always network-based and passive: it analyses a copy of the traffic without being in the data path, so it cannot interfere with the operational systems it protects.

IT/OT Convergence

IT/OT convergence is the merging of corporate IT networks with operational technology as OT systems adopt Ethernet, IP and remote access. It brings efficiency and data-driven operations but exposes previously isolated control systems, including rail signaling, to IT-borne threats.

Network Segmentation

Network segmentation divides a network into security zones grouping assets with shared security requirements, with controlled conduits between them. In IEC 62443 terms, segmentation limits how far an intrusion can spread; a policy violation is traffic crossing zones in a way the operator has not permitted.

OT Asset Inventory

An OT asset inventory is a continuously maintained record of every device on an operational network: its type, vendor, model, firmware, protocols and communication relationships. In rail OT it is the foundation for vulnerability management, segmentation design and compliance evidence.

OT Security

OT (Operational Technology) security is the protection of the hardware and software that monitor and control physical processes: in rail, signaling, train control and trackside systems. OT differs from IT in its priorities (safety and availability over confidentiality), decades-long asset lifecycles and specialized protocols.

Passive Network Monitoring

Passive network monitoring analyzes a copy of network traffic, obtained through a SPAN (mirror) port or a network TAP, without injecting any packets into the monitored network. It is the default approach for safety-critical rail systems because it cannot interfere with operations.

Purdue Model

The Purdue Model is a reference architecture for industrial control networks, arranging systems into levels from Level 0 (physical process and sensors) through Levels 1 to 3 (control, supervision and operations) to Levels 4 and 5 (enterprise IT). It is a common basis for segmenting OT from IT.

Safety-Security Co-Engineering

Safety-security co-engineering is the practice of designing, assessing and maintaining a system's functional safety and its cybersecurity together, so that neither undermines the other. In rail it means aligning the security lifecycle of IEC 63452 with the safety lifecycle of EN 50126, 50128 and 50129 from the first risk analysis through decommissioning.

Secure Remote Access

Secure remote access is the set of controls that allow suppliers, maintainers and operators to reach OT systems from outside the operational network without exposing those systems to attack. It covers how connections are authenticated, brokered, restricted in scope and time, recorded and monitored.

Vulnerability Management (OT)

Vulnerability management in OT is the continuous process of identifying known weaknesses in operational assets, assessing the risk they pose in context and deciding how to treat them. In rail, patching is often impossible or slow because of safety certification, so the emphasis shifts to visibility, prioritisation and compensating controls.

Zones and Conduits

Zones and conduits are the IEC 62443 method for partitioning an OT system for security. A zone groups assets that share the same security requirements; a conduit is the controlled communication path between zones. Each zone is assigned a target security level based on a risk assessment, and conduits enforce what may cross the boundary.