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A.M. Peak Period: (See also P.M. Peak Period) The period in the morning when additional services are provided to handle higher passenger volumes. The period begins when normal, scheduled headways are reduced and ends when headways return to normal. (FTA1)

A/C: Aircraft (FAA8)

A/DACG: Arrival / Departure Airfield Control Group (MTMC1)

A/G: Air - To - Ground (FAA19)

A/I: Accident/Incident (FRA4)

A3: Automatic Three Speed (DOE6)

A4: Automatic Four Speed (DOE6)

A5: Automatic Five Speed (DOE6)

AAA: American Automobile Association (FHWA11)

AAA: Automated Airlift Analysis (MTMC1)

AAC: Advanced AERA Concepts (FAA17)

AAC: Mike Monroney Aeronautical Center (FAA7)

AADC: Approach and Departure Control (FAA16)

AADT: Annual Average Daily Traffic (FHWA8)

AAF: Army Airfield (FAA17)

AAI: Arrival Aircraft Interval (FAA4)

AAIA: Airport and Airway Improvement Act (OST3)

AAL: American Airlines (FAA18)

AALPS: Automated Air Load Planning System (MTMC1)

AAMA: American Automobile Manufacturers Association (BTS8)

AAMVA: American Association of Motor Vehicle Administrators (FHWA10) (NHTSA6)

AAN: Air Ambulance Network (MTMC1)

AAP: Advanced Automation (FAA17)

AAPA: American Association of Port Authorities (MARAD4)

AAR: Airport Acceptance Rate (FAA4) (FAA8)

AAR: Association of American Railroads (BTS2) (MTMC1) (RSPA1)

AAS: Advanced Automation System (FAA17) (FAA7) (FAA8)

AAS: Airport Advisory Service (FAA2)

AASHTO: American Association of State Highway and Transportation Officials (FHWA7) (FHWA8)

AAWDT: Annual Average Weekday Traffic (TRB1)

ABA: American Bus Association (ENO1)

Abaft: A point beyond the midpoint of a ship's length. (MARAD2)

Abandoned Runway: Intact but not maintained or intended for use runway. (DOI3)

Abbreviated Injury Scale: An integer scale developed by the Association for the Advancement of Automotive Medicine to rate the severity of individual injuries. (NHTSA2)

Abbreviated Instrument Flight Rules (IFR) Flight Plans: An authorization by Air Traffic Control (ATC) requiring pilots to submit only that information needed for the purpose of ATC. It includes only a small portion of the usual Instrument Flight Rules (IFR) flight plan information. In certain instances, this may be only aircraft identification, location, and pilot request. Other information may be requested if needed by ATC for separation/control purposes. It is frequently used by aircraft which are airborne and desire an instrument approach or by aircraft which are on the ground and desire a climb to Visual Flight Rule (VFR)-on-top. (FAA4)

Abeam: An aircraft is "abeam" a fix, point, or object when that fix, point, or object is approximately 90 degrees to the right or left of the aircraft track. Abeam indicates a general position rather than a precise point. (FAA4)

Abort: To terminate a preplanned aircraft maneuver; (e.g., an aborted takeoff). (FAA4)

ABQ: Albuquerque International Airport (FAA11)

ABS: American Bureau of Shipping (MARAD4)

ABS: Antilock Braking System (NHTSA5)

ABS: Automatic Block Signal (TRB1)

Absolute Block: A block in which no train is permitted to enter while it is occupied by another train. (49CFR218)

ABYC: American Boat and Yacht Council (USCG1)

AC: Advisory Circular (FAA19) (FAA12)

AC: Air Controller (MTMC1)

AC: Aircraft (MTMC1)

AC: Aircraft Commander (MTMC1)

AC: Airframe Change (MTMC1)

AC: Alcohol Concentration (49CFR383)

AC: Asphalt Concrete (FHWA7)

ACAIS: Air Carrier Activity Information System (BTS7) (FAA11)

ACARS: Automatic Communications Addressing and Reporting System (FAA17)

ACAS: Airborne Collision Avoidance System (FAA7)

ACC: Air Center Commander (MTMC1)

ACC: Aircraft Commander (MTMC1)

ACC: Area Control Center (FAA4)

ACC/INC: Accident/Incident (FRA4)

ACCC: Area Control Computer Complex (FAA17) (FAA8)

Accelerate Stop Distance Available: The runway plus stopway length declared available and suitable for the acceleration and deceleration of an airplane aborting a takeoff. (FAA4) (FAA12)

Acceleration Power: Measured in kilowatts. Pulse power obtainable from a battery used to accelerate a vehicle. This is based on a constant current pulse for 30 seconds at no less than 2/3 of the maximum open-circuit-voltage, at 80% depth-of-discharge relative to the battery's rated capacity and at 20 degrees Celsius ambient temperature. (DOE6)

Access Restrictions Road Gate: Constraints on use. (DOI3)

Access Rights: This element identifies who has acquired legal access rights over a road segment. (DOI2)

Accessible Stations: A public transportation passenger facility which provides ready access, is useable, and does not have physical barriers that prohibit and/or restrict access by individuals with disabilities, including individuals who use wheelchairs. (FTA1)

Accessible Vehicles: Public transportation revenue vehicles which do not restrict access, are usable, and provide allocated space and/or priority seating for individuals who use wheelchairs. (FTA1)

Accessory or Auxiliary Equipment: A particular item of equipment added to a vehicle to aid or contribute to the vehicle's operation and/or mission. (GSA2)

Accident: See also Casualty, Collision, Crash, Derailment, Event, Fatality, Incident, Injury, Jackknife, Rollover, Third Party, Truck Crash, Type of Occurrence.

Accident: Includes continuous or repeated exposure to the same conditions resulting in public liability which the insured neither expected nor intended. (49CFR387)

Accident: An occurrence involving a commercial motor vehicle operating on a public road which results in one of the following: a fatality; bodily injury to a person, who as a result of the injury, immediately receives medical treatment away from the scene of the accident; or one or more motor vehicles incurring disabling damage as a result of the accident, requiring the vehicle to be transported away from the scene by a tow truck or other vehicle. It does not include: an occurrence involving only boarding and alighting from a stationary motor vehicle; an occurrence involving only the loading or unloading of cargo; or an occurrence in the course of the operation of a passenger car or a multipurpose passenger vehicle, as defined in 49 CFR 571.3, by a motor carrier and is not transporting passengers for hire or hazardous materials of a type and quantity that require the motor vehicle to be marked or placarded in accordance with 49 CFR 177.823. (49CFR390)

Accident: 1) An event that involves the release of gas from a pipeline or of liquefied natural gas or gas from an LNG facility resulting in a death, or personal injury necessitating in-patient hospitalization; or estimated property damage, including cost of gas lost, of the operator or others, or both, of $50,000 or more; 2) an event that results in an emergency shutdown of an LNG facility; 3) an event that is significant, in the judgment of the operator, even though it did not meet the criteria of 1) or 2). (AGA1)

Accident: An incident involving a moving vehicle. Includes collisions with a vehicle, object, or person (except suicides) and derailment/left roadway. (FTA2)

Accident: Occurrence in a sequence of events that produces unintended injury, death or property damage. Accident refers to the event, not the result of the event. (NSC1)

Accident Classes: Used to categorize commercial vehicle accidents according to accident severity (i.e., fatal accidents, injury accidents, and property damage accidents). (FHWA4)

Accident Consequences: The physical results of motor vehicle accidents. Consequences include fatalities, injuries, and property damage. (FHWA2) (FHWA4)

Accident Severity: Measures the seriousness of an accident according to the type and quantity of the accident's consequences. Fatalities are more severe than injuries, and injuries are more severe than property damage. (FHWA2) (FHWA4)

Accident Type: An accident type is classified as either "collision" or "non-collision." (FHWA2) (FHWA4)

Accident/Incident: 1) Any impact between railroad on-track equipment and an automobile, bus, truck, motorcycle, bicycle, farm vehicle or pedestrian at a rail-highway grade crossing; 2) Any collision, derailment, fire, explosion, act of God, or other event involving operation of railroad on-track equipment (standing or moving) that results in more than $6,300 in damages to railroad on-track equipment, signals, track, track structures, and road-bed; 3) Any event arising from the operation of a railroad which results in: i) Death of one or more persons; ii) Injury to one or more persons, other than railroad employees, that requires medical treatment; iii) Injury to one or more employees that requires medical treatment or results in restriction of work or motion for one or more days, one or more lost work days, transfer to another job, termination of employment, or loss of consciousness; or iv) Occupational illness of a railroad employee as diagnosed by a physician. (49CFR225)

Accounting Changes Income (Loss): The difference between the amount of retained earnings at the beginning of the period in which a change in accounting has occurred and the amount of retained earnings that would have been reported, net of applicable taxes, at that date if the new accounting had been applied retroactively for all applicable periods. (BTS4)

ACD: Engineering, Research and Development Service (FAA17)

ACDO: Air Carrier District Office (FAA4)

ACE: Airport Capacity Enhancement (FAA17)

ACF: Area Control Facility (FAA17) (FAA19) (FAA8)

ACHP: Advisory Committee On Highway Policy (MTMC1)

ACIP: Airport Capital Improvement Program (OST3)

Acknowledging Device: A manually operated electric switch or pneumatic valve by means of which, on a locomotive equipped with an automatic train stop or train control device, an automatic brake application can be forestalled, or by means of which, on a locomotive equipped with an automatic cab signal device, the sounding of the cab indicator can be silenced. (49CFR236)

Acknowledging Time: As applied to an intermittent automatic train stop system, a predetermined time within which an automatic brake application may be forestalled by means of the acknowledging device. (49CFR236)

Acknowledgment Circuit: A circuit consisting of wire or other conducting material installed between the track rails at each signal in territory where an automatic train stop system or cab signal system of the continuous inductive type with 2-indication cab signals is in service, to enforce acknowledgement by the engineman at each signal displaying an aspect requiring a stop. (49CFR236)

ACLS: Automatic Carrier Landing System (FAA4)

ACLT: Actual Calculated Landing Time (FAA4)

Acrobatic Flight: An intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or abnormal acceleration not necessary for normal flight. (FAA4)

ACSEP: Aircraft Certification Systems Evaluation Program (FAA7)

ACSSP: Air Carrier Standard Security Programs (FAA1)

Active Aircraft: All legally registered civil aircraft which flew one or more hours. (FAA2) (FAA6) (FAA9)

Active Vehicle: Transit passenger vehicles licensed, where required, and maintained for regular use, including spares and vehicles out of service for maintenance purposes, but excluding vehicles in "dead" storage, leased to other operators, in energy contingency reserve status, permanently not usable for transit service, and new vehicles not yet outfitted for active service. (APTA1)

Active Vehicles in Fleet: The vehicles in the year end fleet that are available to operate in revenue service, including vehicles temporarily out of service for routine maintenance and minor repairs. (FTA1)

ACTS: American Coalition for Traffic Safety, Inc. (MM)

Actual Calculated Landing Time (ACLT): A flight's frozen calculated landing time. An actual time determined at freeze calculated landing time (FCLT) or meter list display interval (MLDI) for the adapted vertex for each arrival aircraft based upon runway configuration, airport acceptance rate, airport arrival delay period, and other metered arrival aircraft. This time is either the vertex time of arrival (VTA) of the aircraft or the tentative calculated landing time (TCLT)/actual calculated landing time (ACLT) of the previous aircraft plus the arrival aircraft interval (AAI), whichever is later. This time will not be updated in response to the aircraft's progress. (FAA4)

Actual Service: Total service operated during each time period. Actual service excludes missed trips and service interruptions (e.g., strikes, emergency shutdowns), but includes deadheading. Actual service is measured by vehicles in service, in miles and/or hours. (FTA1)

Actual Severity: On scene evaluation of the degree of danger that existed. An "after-the-fact" evaluation by the reporting unit. (USCG3)

Actual Vehicle Miles/Hours: The miles/hours a vehicle travels while in revenue service (actual vehicle revenue miles/hours) plus deadhead miles/hours. For rail vehicles, vehicle miles/hours refer to passenger car miles/hours. Actual vehicle miles/hours exclude miles and hours for charter services, school bus service, operator training and maintenance testing. (FTA1)

Ad Valorem: A charge levied on persons or organizations based on the value of transaction. It is normally a given percentage of the price at the retail or manufacturing stage and is a common form of sales tax; e.g. Federal excise tax on new trucks and trailers. (ATA2)