Appendix D GLOSSARY OF CONTROL TERMS

The language of rail and train con- False Restrictive Aspect—the aspect of a sig- trol technology contains many specialized terms nal that conveys an indication more restric- that may be unfamiliar to the general reader. This tive than intended. glossary has been prepared as an aid to understand- ATTENDANT-a transit employee on board a ing the terminology used in the report. It is also con- train in service whose principal duties are to templated that the glossary may be useful as a oversee safety, provide security, and assist in reference for additional reading on the subject of emergency situations (as distinct from a train ATC and transit system engineering. For this operator, motorman, who is responsible for run- reason, the list of terms defined here has been ex- ning the train). panded to include some background items not needed for the immediate purpose of reading this AUDIBLE CAB INDICATOR-an alerting device, report. on a train equipped with cab signals, designed to sound when the cab signal changes and to con- The principal source of the definitions presented tinue sounding until acknowledged. (See here is the Lexicon of Rail Rapid Transit Safety- Acknowledging Device.) Related Terminology, prepared by the Safety Tech- nology Applied to Rapid Transit (START) Commit- AUDIO-FREQUENCY CIRCUIT—a track tee of the American Public Transit Association, circuit energized by an electrical current alter- January 1975. The START Lexicon, in turn, draws nating in the audio-frequency range extensively on earlier work by the Association of (15,000-20,000 Hz); also called “high frequency” American Railroads and the U.S. Department of or “overlay” . Transportation. In addition to START, other AUTOMATIC BLOCK SIGNAL SYSTEM—a sources consulted include General Order No. 127 of series of consecutive blocks governed by block the Public Utilities Commission of the State of signals, cab signals, or both, actuated by occupan- California, August 1967, and several technical cy of the track or by certain conditions affecting specifications prepared by WMATA. In all cases, the use of a block; such as an open switch or a car however, the responsibility for interpretation and for the accuracy and completeness of the defini- standing on a turnout and blocking the main track. (See also Block and Manual Block Signal tions offered here rests with the authors of this report. System.) AUTOMATIC CAR IDENTIFICATION—a ACKNOWLEDGING DEVICE—a manual device system that automatically provides positive used by the train operator to forestall automatic recognition and transmission of individual car brake application on a train equipped with numbers as they pass a fixed wayside point. automatic or to silence the sounding of a cab indicator on a train equipped with cab sig- —the method naling. (See Audible Cab Indicator.) (and, by extension, the specific system) for automatically controlling train movement, en- ASPECT—the visual indication presented to an ap- forcing train safety, and directing train opera- proaching train by a wayside signal; also, the dis- tions. ATC includes four major functions: play presented by a cab signal to an operator in Automatic Train Protection (ATP)--assuring the cab. The aspect is said to be “clear” (proceed safe train movement by a combination of at civil speed) or varying degrees of “restrictive.” train detection, separation of running False Clear Aspect—the aspect of a signal that on the same track or over interlocked conveys an indication less restrictive than routes, overspeed prevention, and route in- intended. terlocking.

207 Automatic Train Operation (ATO)--controll- rate of the vehicle is less than the braking rate re- ing speed, programed station stopping, door quested by the automatic train control system. operation, performance level modification, BRAKING—the process of retarding or stopping and other functions traditionally assigned train movement by any of various devices: to the train operator and conductor. Dynamic Braking—a system of electrical Automatic Train Supervision (ATS)— braking in which the traction motors are monitoring of system status and directing used as generators and convert the kinetic traffic movement to maintain the schedule energy of the vehicle into electrical energy, or minimize the effect of delays. which is consumed in resistors and, in so Communication (CS)—interchanging infor- doing, exert a retarding force on the vehi- mation (voice, data, or video) between cle. system elements separated by distance. Friction Braking—braking supplied by a AVAILABILITY—the portion of time that a mechanical shoe or pad pressing against the system is operating or ready for operation; wheels or other rotating surface; also called mathematically, the probability that a system or “mechanical braking. ” system element will be operational when re- Regenerative Braking-a form of electrical quired, expressed as the ratio of mean time be- braking in which the current generated by tween failure to the sum of mean time between the traction motor is returned to the trac- failure plus mean time to restore. [A = tion power supply for use in propelling MTBF/(MTBF + MTTR)] (See also Mean Time other trains. (In ordinary dynamic braking Between Failure and Mean Time to Restore.) the generated power is dissipated in resis- BASE PERIOD—the nonrush hour period of week- tors.) day transit system service. (See also Peak There are two methods of controlling Period,) brake application: BERTH—the space assigned for a train of specified Closed-Loop Braking-continuous modula- length when stopped at a station platform or in a tion (by means of feedback) under the terminal zone. (See Terminal Zone.) direction of the automatic train operation BERTHING—the positioning of a train in its system or the human operator. (See Closed- assigned berth. Loop Principle,) BLENDING—the automatic and simultaneous ap- Open-Loop Braking—braking without plication of dynamic and friction braking, where modulation through feedback from the the effort of each is continuously proportioned to ATO system. achieve the required total braking effect. BRAKING EMERGENCY—irrevocable unmodu- BLOCK—a length of track of defined limits, the use lated (open-loop) braking to a stop usually at a of which is governed by block signals, cab sig- higher rate than that obtained with a full service nals, or both. brake application. Absolute Block-a block into which no train is BRAKING, FULL SERVICE-a nonemergency allowed to enter while it is occupied by brake application that obtains the maximum another train. brake rate consistent with the design of the pri- Permissive Block--a block into which a train mary brake system. Full service braking can be is allowed to enter even though occupied by released and reapplied. another train. BRAKING, SERVICE-braking produced by the BLOCK SIGNAL-See Signal. primary train braking system, BRAKE ASSURANCE—the function provided by CAB SIGNAL SYSTEM—a signal system whereby a subsystem within the automatic train operation block condition and the prevailing civil speed system that will cause the emergency brakes of a commands are transmitted and displayed directly vehicle to be applied when the actual braking within the train cab. The cab signal system may

208 be operated in conjunction with a system of fixed slower than the following train. (See also Closing wayside signals or separately. (See also Signal.) up.) CATENARY—the wire or wires above the track CLOSING UP—running a following train to a posi- (including the messenger, supports, and insula- tion that will allow it to couple with a stopped tion) that carry electric energy for the propulsion leading train. of trains. (See also Contact Rail.) COAST—the moving condition of a car or train CENTRAL CONTROL—the place from which where the propulsion is inactive and, usually, a train supervision and direction is accomplished certain minimum braking is applied. (See also for the entire transit system; the train command Freewheeling.) center. CONDUCTOR-an attendant whose main func- CIRCUIT, TRACK-an arrangement of electrical tion is to operate train doors. equipment, including the rails of the track, that CONSIST (noun)—the number, type, and specific forms a continuous electrical used for the identity of cars that compose a train. purpose of detecting the presence of trains on the rails; the track circuit may also be used to com- CONTACT RAIL-a rail, mounted on insulators municate commands or other information be- alongside the running rails, that provides electric tween the wayside and the train. energy for the propulsion of trains. (Also known as “.”) Check-In/Check-Out—a track circuit system that detects the entrance of the front end of CROSSOVER—two turnouts, arranged to form a a train into a block and the departure of the continous passage between two parallel tracks. rear end of a train from a block for the pur- DEADMAN CONTROL-a safety device that re- pose of determining block occupancy. quires continuous pressure or activity to remain Coded Track Circuit—a track circuit in which activated; used to detect the inattention or dis- the feed energy is varied or interrupted ability of a train operator. periodically for the purpose of transmitting DEPARTURE TEST-an operational test made in commands or instructions to the train or a yard or on a transfer track before permitting the operating train detection apparatus. unit to enter revenue service. Fail-Safe Circuit-a circuit designed to princi- DISPATCH—to start a train into revenue service ples which will cause the actuated device to from a terminal zone, transfer track, or desig- assume its most restrictive position (or a nated intermediate point. state generally known to be safe) when any element of the circuit or system fails. DISPATCHER-a person at central control whose Vital Circuit--an electrical circuit that affects function is to dispatch trains, monitor train the safety of train operation. operation, and to intervene in the event of schedule disruption or when any change in serv- CIVIL SPEED-See Speed Limit. ice or routing is required. (Also called “Line Supervisor” or “Central Supervisor.”) CLOSED-CIRCUIT PRINCIPLE—the principle of circuit design employing a circuit that is nor- DOWNSTREAM—for a given direction of travel, mally energized and, on being deenergized or in- locations that will be reached after passing a terrupted, causes the controlled function to given point (equivalent to the AAR term “in ad- assume its most restrictive condition. vance of”).

CLOSED-LOOP” PRINCIPLE—the principle of DWELL (or DWELL TIME)—the elapsed time control system design in which the response of a from the instant a train stops moving in a station system (feedback) is continuously compared until the instant it resumes moving, with the controlling signal to generate an error signal. ENTRANCE—EXIT ROUTE CONTROL—a system of control that automatically CLOSING IN—running a following train toward a alines switches and clears signals to form a train leading train that is either stopped or running route in response to manual inputs designating

209 the entrance and exit points of the desired route. IMPEDANCE BOND-a device of low resistance (Also called “N-X.”) and relatively high reactance, used to provide a continuous path for the return of propulsion cur- FACING MOVEMENT—the movement of a train rent around insulated joints and to confine alter- over points of a switch which face in the direc- nating current signaling energy within a track tion in which the train is moving. (See also Trail- circuit. ing Movement.) INDUCTIVELY COUPLED IMPEDANCE FAIL-SAFE--a characteristic of a system which BOND--an impedance bond in which transmit- ensures that a fault or malfunction of any ele- ter energy and receivers are inductively coupled ment affecting safety will cause the system to into a track circuit, revert to a state that is known to be safe; alter- natively, a system characteristic which ensures INSULATED JOINT-a joint placed between abut- that any fault or malfunction will not result in an ting rail ends to insulate them from each other unsafe condition. electrically. FALSE OCCUPANCY--an indication of track oc- INTERLOCKING--an arrangement of signals and cupancy when no train is present. control apparatus so interconnected that functions must succeed each other in a predetermined se- FREEWHEELING-a mode of operation in which quence, thus permitting train movements along the train is allowed to roll freely without tractive routes only if safe conditions exist. or braking effort being applied. (See also Coast.) Automatic Interlocking-an interlocking con- FREQUENCY SHIFT KEYED (FSK)--a technique trolled by logic circuits so that movements used with high-frequency a.c. track circuits, in succeed each other in proper sequence which the frequency of the track signal is varied without need for manual activation or con- between two or more discrete states to convey trol. information (used as an alternative to rate modulation where the track circuit is turned on Manual Interlocking—an interlocking oper- ated manually from an interlocking and off as an information code). machine, so interconnected (either FROG-a track structure, used at the intersection mechanically or electrically) that move- of two running rails, to provide support for ments succeed each other in proper sequen- wheels and passageway for their flanges, thus cy. permitting wheels on either rail to cross the other. A frog may either be fixed or have mova- Relay Interlocking-an interlocking in which ble points like a switch. locking is accomplished electrically by in- terconnection of relay circuits. GATE—the limit of an interlocked route where en- try to that route is governed by a signaling INTERLOCKING LIMITS—the length of track be- device. 102 tween the most remote opposing home signals of Fixed Gate--the limit of an interlocked route an interlocking. beyond which automatic operation of trains INTERLOCKING MACHINE-an assemblage of is never permitted. manually operated levers or like devices for con- HEADWAY—the time separation between two trolling the switches, signals, and other apparatus trains traveling in the same direction on the same of an interlocking. (Also called “Switch track, measured from the instant the head end of Machine,”) the leading train passes a given reference point until the head end of the train immediately INTERLOCKING ROUTE-a route between two following passes the same reference point. opposing interlocking signals. HOSTLER-an employee assigned to operate cars JERK—the rate of change of acceleration (the or trains manually within the yard or mainte- second derivative of velocity), expressed in units nance area. of miles per hour per second per second 2 Hz (HERTZ)—the unit of frequency equal to 1 (mphpsps, mph/see/see, or mph/sec ). cycle per second. -a location where train routes con- verge or diverge. lo2Tht,sf,,. terms ;] rp pet; II 1 ia r to the BA RT s~st[’m.

210 KEY-BY—the act of lowering a trip stop in order to for any conflicting route) until expiration of pass a signal displaying a stop indication; so a predetermined time interval after a signal called because of the use at one time of a key by is restored to its most restrictive indication. the train operator to actuate the mechanism for Traffic Locking--electric locking which pre- lowering the trip stop. Key-by today operates vents the actuation of devices for changing automatically without a key, the direction of traffic on a section of track LOCKING-establishing an electrical or mechani- while that section is occupied or while a cal condition for a switch, interlocked route, signal displays an aspect for a movement to speed limit, or automatic function such that its proceed into that section, state cannot be altered except by a prescribed Sectional Release Locking—a route locking so and inviolate sequence of actions. arranged that, as a train clears a section of the route, the locking affecting that section Approach Locking-electric locking effective is released. (Also called “Trailing Release while a train is approaching within a Locking.”) specified distance a signal displaying an aspect to proceed and which prevents, until MAINTAINABILITY—the property of a system after the expiration of a predetermined that allows it to be repaired and restored to time interval after such signal has been operating condition after a component malfunc- caused to display its most restrictive aspect, tion or failure; maintainability is often expressed the movement of any interlocked or as mean time to restore (or repair). electrically locked switch, movable point MANUAL BLOCK SIGNAL SYSTEM-a block frog or in the route governed by the signal system operated manually, usually based signal and which prevents an aspect to pro- on information transmitted by telephone or ceed from being displayed for any conflict- telegraph. ing route. Electric Locking—an electrical circuit arrange- MARRIED PAIR—two semipermanently coupled ment by means of which levers of an in- cars that share certain essential components and terlocking machine, switches, or other sig- are usually operated as a unit. nal apparatus is secured against operation MASTER CONTROLLER-a carborne device that under prescribed conditions. generates control signals to the propulsion and Indication Locking-electric locking which braking systems, prevents actions that would result in an un- safe condition for a train movement if a sig- MEAN TIME BETWEEN FAILURES (MTBF)— nal, switch, or other operative unit fails to the average time that a system or component will make a movement corresponding to that of operate without fai1ure or ma1function; its control. mathematicaly, MTBF = (operating time) /(number of failures). MTBF is the measure Occupancy Detector Locking--electric locking of reliability. which prevents the movement of a track switch while the track circuit or circuits MEAN TIME TO RESTORE (MTTR)—the surrounding that switch are occupied by a average time required to restore a system or com- train. ponent to operation after a failure; this time is Route Locking—electric locking, effective measured from the time troubleshooting and when a train passes a signal displaying an repair work is begun until the system or compo- nent is again operable; mathematically, aspect for it to proceed, that prevents the MTTR = (cumulative corrective maintenance movement of any switch in the route governed by the signal and prevents the time) /(number of failures). MTTR is the measure of maintainability, clearing of a signal for any conflicting route. MODEL BOARD-a reproduction of the track Time Locking-electric locking that prevents assemblage (not necessarily to scale) equipped the operation of any switch in the route (or with lights and other indicators, used for the pur-

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72-683 C) - 76 - 15 pose of train supervision and traffic control (Also overhead electric line by means of pantograph or called “Train Board”). from an electrified third rail. Rail rapid transit may use steel wheels on steel rails or pneumatic MOTORMAN-See Operator. tires on wooden, steel, or concrete guideway. MTBF-See Mean Time Between Failures. RELAY-a device operated by variation in the con- MTTR-See Mean Time to Restore. dition of one electric circuit and used to effect the operation of other devices in the same or NORMAL DIRECTION—the prescribed direction another circuit; commonly, an electromagnetic of train traffic as specified by the rules; usually, device to achieve this function. the direction in which all regularly scheduled revenue service operations are conducted. Track Relay--a relay receiving all or part of its operating energy through conductors N–X-See Entrance-Exit Route Control. having the track rails as an essential part. OPERATOR—the transit employee on board the Vital Relay—a relay, meeting certain train having direct and immediate control over stringent specifications, designed so that the movement of the train. (Also called “Motor- the probability of its failing to return to the man.”) prescribed state after being deenergized is OPPOSING TRAIN—a train moving in the direc- so low as to be considered, for all practical tion opposite to another train on the same track. purposes, nonexistent. OVERSPEED CONTROL—that onboard portion RELIABILITY—the probability that a system or of the carborne ATC system that enforces speed component thereof will perform its specified limits in a fail-safe manner. function without failure and within prescribed limits; reliability is often expressed as a mean PABX—a designation used in the national failure rate (MTBF). telephone system to denote a privately owned telephone system that operates by the use of dial- REVENUE SERVICE—transportation of fare- ing, such as that used in some transit systems for paying passengers on main line routes. communication between stations or wayside REVERSE DIRECTION—train movement op- locations and central control. posite to the normal direction. (See Normal PEAK PERIOD—the period during a weekday Direction.) when system demand is highest; usually REVERSE RUNNING-operation of a train in the 7:30-9:30 a.m. and 4:30-6:30 p.m. (Also called reverse direction. “Rush Hour.”) (See also Base Period) ROUTE-a succession of contiguous blocks be- POINT-See Switch Point. tween two controlled gates or interlocked sig- nals. PROPERTY—literally, the right-of-way, track, structures, stations, and facilities owned or oper- Conflicting Routes—two or more routes (op- ated by a transit agency; but used generally as a posing, converging, or intersecting) over synonym for the operating agency itself. (See which movements cannot be made also Territory.) simultaneously without possibility of colli- RAIL RAPID TRANSIT—a mode of transporta- sion. tion operating in a city or metropolitan area and Normal Route--a prescribed route, a route in high-speed speed passenger cars run singly or in the normal direction of train travel. trains on fixed guideways in separate rights-of- way from which all other vehicular and foot Reverse Route--a route opposite to the normal traffic is excluded. Tracks may be located in un- route. derground tunnels, on elevated structures, in ROUTE REQUEST—registration at an interlocking open cut, or at surface level. There are very few, of a desired interlocked route. if any, grade crossings; and rail traffic has the right-of-way at such intersections. Cars are RUNTHROUGH—intentionally passing a station driven electrically with power drawn from an platform without making a scheduled stop.

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SEMAPHORE-a wayside signal device by which SLIP-SLIDE SYSTEM-an onboard system for indications are given by the position of a mova- automatically detecting and correcting slip and ble arm in daylight hours and by the color of a slide by making compensating adjustments of light in darkness. propulsion and braking to maintain optimum traction (wheel-rail adhesion), SHUNT-a conductor joining two points in an electrical circuit so as to form a parallel or alter- SPEED nate path through which a portion of the current Civil Speed (Limit)—the maximum speed may pass. allowed in a specified section of track as determined by physical limitations of the SHUNTING SENSITIVITY-the maximum impe- track structure, train design, and passenger dance that, when placed at the most adverse comfort. shunting location, will cause the track circuit to indicate the presence of a train. Safety Speed (Limit)—the maximum speed at which a train can safely negotiate a given —a track auxiliary to the main track, used section of track under the conditions pre- for meeting, passing, or storing trains. vailing at the time of passage. (Safety speed may be less than or equal to civil speed,) SIGNAL-a means of communicating direction or warning. Schedule Speed-the speed at which a train must operate to comply with the timetable; Block Signal-a fixed signal at the entrance of mathematically, the distance from terminal a block governing trains entering and using to terminal divided by the time scheduled that block, for the trip (including station stops), Cab Signal--a signal in the train operator’s SPEED PROFILE-a plot of speed against distance cab that governs the movement of that train traveled. by conveying the automatic block aspects SPEED REGULATOR-an onboard subsystem, and the prevailing speed command. usually part of the automatic train operation Clear Signal--a signal displaying the aspect (ATO) system, that controls acceleration and indicating to proceed. braking to cause the train to reach and maintain a desired speed within a given tolerance, Home Signal-a fixed signal at the entrance of a route or block governing trains entering SPIN-See Slip. and using that route or block. STOP Opposing Signals-wayside signals governing train movements in opposite directions over Emergency Stop-stopping of a train by an ap- the same stretch of track. plication of the , which— after initiation-cannot be released until Time Signal-a signal that controls train the train has stopped. speed by requiring that a certain time elapse between entering and leaving a Full Service Stop-a train stop achieved by a block. brake application, other than emergency, Wayside Signal-a signal of fixed location that develops the maximum brake rate. along the track right-of-way. Penalty Stop--irrevocable open-loop braking SIGNAL ASPECT-See Aspect. initiated by an onboard automatic system or by a wayside trip stop as a result of a SLIDE (WHEEL)—the condition, during braking or block violation or uncorrected overspeed. deceleration, where the surface speed of the wheel is less than train speed, Programed Stop-a train stop produced by SLIP (WHEEL)—the condition, during accelera- closed-loop braking such that the train is tion, where the surface speed of the wheel is stopped at a designated point according to a greater than train speed. (Also called “Spin.”) predetermined speed-distance profile.

213 Stop Signal--a signal indication requiring a TRACK CIRCUIT—(See Circuit, Track,) train to stop and stay stopped and permit- TRAFFIC REGULATION--a train supervisory ting no exceptions such as running at function making use of changes in dwell time, reduced speed, movement within restrict- performance level, acceleration rates, or other ing limits, or similar alternatives. train performance characteristics to maintain in- Train Protection Stop-a train stop initiated tended traffic patterns and system stability, by the automatic train protection (ATP) TRAIN-a consist of one or more cars combined system. into an operating unit, (See also Consist.) SWITCH—a device that moves rails (switch TRAIN BOARD—(See Model Board.) points) laterally to permit a train to transfer from one track to another. (See also Frog,) TRAIN DETECTION EQUIPMENT—the track Facing Point Switch-a track switch with circuits and associated apparatus used to detect points facing toward approaching traffic. the presence of trains in blocks, Trailing Point Switch-a track switch with TRAIN IDENTIFICATION-a method of desig- points facing away from approaching nating trains by means of such information as traffic. train number, destination, or length; may be ac- SWITCH POINT-a movable tapered track rail, complished automatically for functions such as with the point designed to fit against the stock routing or dispatching. rail. TRAIN ORDERS—instructions used to govern the TERMINAL ZONE-a length of track, within movement of trains manually, usually written and hand-delivered, which the prescribed running direction can be reversed while it is occupied by a train, TRANSFER ZONE-a zone where changeover TERRITORY—that portion of a route or route net- from manual to automatic operation, or vice ver- work characterized by a particular mode of sa, may be made. (See also Transfer Track, under Track.) operation or type of equipment, e.g., cab signal territory, multiple track territory, TRIP STOP-a mechanical arm, located on the THIRD RAIL-See Contact Rail. wayside, that can initiate a penalty brake ap- plication on a train that passes it by engaging a TRACK brake-triggering device (trip cock) on the train. Double Track—two parallel tracks, usually Trip stops may be fixed, i.e., permanently posi- with each reserved for running in one tioned in the tripping position; or they may be direction only. raised and lowered in response to signal indica- tions, Main Track-a track extending through yards and between stations, upon which trains TURNBACK POINT-a point along the track, not are operated in revenue service or the use at a terminal, where a train may reverse direction of which is governed by signals. if allowed by the train control system, (See also Terminal Zone,) Reversible Track--a section of track on which the prescribed direction of running can be TURNOUT-an arrangement of switch points and reversed if it is unoccupied and the oppos- frog with closure rails that permits trains to be ing home signals are at stop. diverted from one track to another, Single Track--a main track on which trains UPSTREAM—track locations that, for a given are operated in both directions. reference point and direction of travel, lie behind the train and have been passed by it. Transfer Track-a track in a yard area where transfer between main track and yard YARD-a network of tracks for making up trains modes of operation takes place. and storing cars.

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