FRA Signal Employee key terms

The relationship stating that voltage equals current multiplied by resistance (V = I × R); used to calculate expected current, voltage drop, or resistance in signal circuits during troubleshooting and testing.

Two basic ways components connect: in series, current is the same through each element and voltages add; in parallel, voltage is the same across elements and currents add. Determines how a fault affects the whole circuit.

The reduction in voltage across a component or conductor caused by resistance; excessive drop in long track leads or rail can prevent relays and track circuits from operating reliably.

A relay designed so that failure modes (stuck armature, welded contacts, reversed polarity, spring failure) result in the safe, restrictive state; the foundation of conventional fail-safe signal logic.

The design philosophy that any component failure, loss of power, or fault must cause the signal system to display its most restrictive indication or place equipment in the safe state.

Circuit or software logic whose failure cannot produce an unsafe (permissive) output; verified through design and testing so that no single fault yields a false clear or false proceed indication.

A deliberate low-resistance connection across the rails or a circuit element; in track circuits it simulates a train to prove occupancy detection, and in metering it diverts current around a meter.

An electrical circuit using the running rails as conductors to detect the presence of a train; a train's wheels and axles short the rails and drop the track relay, showing occupancy.

The relay energized through the track circuit that picks up when the track is clear and drops away when rails are shunted or the circuit is broken; its state feeds signal and interlocking logic.

A rail joint fitted with insulating material that electrically separates adjacent track circuits or signal blocks so each circuit can detect occupancy independently.

A condition where a foreign object, debris, or poor rail contact provides an unintended shunt path or prevents a train shunt from being detected, causing false clear or false occupancy indications.

The ability of a track circuit, through rail continuity and current flow, to detect a broken rail within its limits and cause a restrictive indication rather than a false clear.

An intersection where a public or private roadway crosses railroad tracks at grade, protected by warning devices such as flashing lights, gates, and bells to warn motorists and pedestrians of approaching trains.

The track circuit or predictor system that detects an approaching train and starts the warning devices at the required time based on train speed and crossing geometry.

The track circuit within the crossing itself, between the approach circuits, that keeps warning devices active while a train occupies the crossing and releases them after the train clears.

An arrangement of signals and switches interconnected so their movements must succeed one another in a predetermined order, preventing conflicting routes from being established simultaneously.

The condition in an interlocking that holds switches and signals in a route until the route is released, preventing switches from moving under a train or a conflicting route from being set.

A device mechanically linked to a switch point that proves the switch is properly positioned and locked before the interlocking permits a signal to clear over that route.

The federal regulations governing rules, standards, and instructions for railroad signal systems, including inspection, testing, and maintenance requirements for signal equipment.

Required scheduled examinations of signal apparatus and circuits at intervals set by regulation, documented to show the equipment was inspected, tested, and found within specified limits.

The written or electronic record documenting signal inspections, tests, results, and corrective actions, retained as required and made available for inspection by regulators and railroad personnel.

The process of correcting a reported signal defect or failure, including making the equipment safe, repairing or replacing components, retesting, and recording the corrective action taken.

Federal regulations requiring railroads to report accidents, incidents, and signal failures to the appropriate authority and to maintain records of those reports and resulting corrective actions.

Federal regulations covering highway-rail grade crossing warning systems, including activation timing, inspection and testing intervals, and reporting of warning system failures.

The set of rules and procedures, including job briefings and lookout or train coordination, that protect employees working on or near tracks from being struck by trains or equipment.

A form of track authority in which a roadway worker is granted exclusive use of a segment of track for a stated period, with trains held clear until the worker releases the authority.

The condition and procedures ensuring workers are protected from train movements, including proper authority, warning time, and clearance from tracks before trains pass.

A procedure for isolating hazardous energy sources by locking the disconnect and attaching a tag identifying the work, ensuring equipment cannot be re-energized while employees are working on it.

Protective gear such as hard hats, safety glasses, high-visibility clothing, gloves, and dielectric footwear worn to reduce injury from electrical, physical, and environmental hazards on signal work.

A sudden release of electrical energy through the air caused by a fault, producing intense heat, light, and pressure; mitigated by de-energizing equipment, proper PPE, and safe work distances.

Safe storage, transport, and disposal of signal-related substances such as batteries, electrolytes, and solvents, following labeling, containment, and spill-response requirements.

The secondary power source, typically a battery bank, that maintains signal and crossing operation during commercial power loss; requires periodic inspection, specific gravity checks, and ventilation.

A processor-based system that enforces speed limits and movement authorities, prevents train-to-train collisions, and protects roadway workers and switches through onboard and wayside components.

Trackside equipment that communicates signal and switch status to the PTC onboard system, enabling enforcement of authorities and restrictions based on the physical signal state.

The permission for a train to move to a specific point, issued by the dispatcher or PTC system and enforced onboard to prevent exceeding limits or entering occupied track.

A track circuit section that is electrically isolated and separately detected, often used at crossings or interlockings to provide distinct occupancy information to signal and warning logic.