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D&H: Dangerous and Hazardous (MARAD2)

D1: First Coast Guard District (Boston, MA) (USCG5)

D11: Eleventh Coast Guard District (Los Angeles, CA) (USCG5)

D13: Thirteenth Coast Guard District (Seattle, WA) (USCG5)

D14: Fourteenth Coast Guard District (Honolulu, HI) (USCG5)

D17: Seventeenth Coast Guard District (Juneau, AK) (USCG5)

D2: Second Coast Guard District (St. Louis, MO) (USCG5)

D5: Fifth Coast Guard District (Portsmouth, VA) (USCG5)

D7: Seventh Coast Guard District (Miami, FL) (USCG5)

D8: Eighth Coast Guard District (New Orleams, LA) (USCG5)

D9: Ninth Coast Guard District (Cleveland OH) (USCG5)

DA: Decision Altitude / Decision Height (FAA4)

DA: Descent Advisor (FAA17)

DAB: Dial-A-Bus (TRB1)

Daily Average Flow: The volume of gas that moves through a section of pipe determined by dividing the total annual volume of gas that moves through a section of pipe by 365 days. Volumes are expressed in million cubic feet per day measured at a pressure of 14.73 psia and a temperature of 60 degrees Fahrenheit. For pipes that operate with bidirectional flow, the volume used in computing the average daily flow rate is the volume associated with the direction of flowing gas on the peak day. (DOE1)

Daily Vehicle Travel: Is the amount of vehicle travel (in thousands) accumulated over a 24-hour day, midnight to midnight, traversed along a "public road" by motorized vehicles, excluding construction equipment or farm tractors. Vehicle travel not occurring on public roads, such as that occurring on private land roads (private roads in parking lots, shopping centers, etc.) must be also be excluded. (FHWA2)

DAIR: Direct Altitude and Identity Readout (FAA4)

DAL: Dallas Love Field (FAA11)

Dam: A barrier constructed across a watercourse to control the flow or raise the level of water. (DOI4)

Dam Bulletin Board: A bulletin board located at certain dams to give stage readings and indicate whether to use lock or go over the dam. "N.P." means use the lock. "P" means go over the dam. Largely obsolete in use since the advent of radio communications. (TNDOT1)

Dam Open: The situation when the gates are open so as to pass water unimpeded. (TNDOT1)

Dam Warning Buoys: Buoys placed above the face of a dam to warn traffic of danger. These buoys may be of peculiar shape and generally have the word "danger" posted on them. (TNDOT1)

Dam/Weir: A barrier constructed to control the flow or raise the level of water. (DOI3)

Danger Area: An airspace of defined dimensions within which activities dangerous to the flight of aircraft may exist at specified times. Note: The term "Danger Area" is not used in reference to areas within the United States or any of its possessions or territories. (FAA4)

Danger Signal: Four or more short blasts of the boat's or lockmaster's whistle to indicate danger or the need for special caution. (TNDOT1)

DAR: Dial-A-Ride (TRB1)

DARC: Direct Access Radar Channel (FAA19)

DART: Dallas Area Rapid Transit (FHWAII)

DASCAR: Data Acquisition System for Crash Avoidance Research (NHTSA5)

DASI: Digital Altimeter Setting Indicator (FAA19)

Datum: Reference point for elevations of structures and water level. (TNDOT1)

Day: From 6 a.m. to 5:59 p.m. (NHTSA3)

DAY: James M Cox Dayton International Airport (FAA11)

Daymark: An unlighted shore aid to navigation, either diamond, square, or triangle shaped. (TNDOT1)

DB: Decibel (BTS8)

DBN: Day Beacon (USCG5)

DBRITE: Digital Bright Radar Indicator Tower Equipment (FAA19) (FAA8)

DC: Direct Current (FAA19)

DCA: Washington National Airport (FAA11)

DCC: Display Channel Complex (FAA19)

DCM: Dangerous Cargo Manifest (RSPA1)

DDPS: Dual Driver Protective Service (MTMC1)

DDT: Deflagration-To-Detonation Transition (RSPA1)

Dead Axle: Non powered rear axle on tandem truck or tractor. (ATA1)

Dead Freight: The freight charges paid by the charterer of a vessel for contracted space which is left partially unoccupied. (TNDOT1)

Dead Heading: Running empty. (ATA1)

Dead Locomotive: A locomotive other than a control cab locomotive that does not have any traction device supplying tractive power; or a control cab locomotive that has a locked and unoccupied cab. (49CFR229)

Dead Reckoning: As applied to flying, the navigation of an airplane solely by means of computations based on airspeed, course, heading, wind direction, speed, groundspeed, and elapsed time. (FAA4)

Dead Section: A section of track, either within a track circuit or between two track circuits, the rails of which are not part of a track circuit. (49CFR236)

Deadhead: Miles and hours that a vehicle travels when out of revenue service. This includes leaving and returning to the garage, changing routes, etc., and when there is no reasonable expectation of carrying revenue passengers. However, it does not include charter service, school bus service, operator training, maintenance training, etc. For non-scheduled, non-fixed-route service (demand responsive), deadhead mileage also includes the travel between the dispatching point and passenger pick-up or drop-off. (FTA1)

Deadhead: 1) Any water-soaked wooden pile, tree, or log that is floating just awash in a nearly vertical position. A menace to small boats and to the propellers of vessels. 2) A tow returning from a trip without barges or with empty barges. (TNDOT1)

Deadhead Transportation: Occurs when an employee is traveling at the direction or authorization of the carrier to or from an assignment, or the employee is involved with a means of conveyance furnished by the carrier or compensated for by the carrier. (FRA2)

Deadman Control: A pedal, handle, or other form of switch, or combination thereof, that the operator must keep in a depressed or twisted position while a rail vehicle (or train) is moving. If the control is released, the power is cut off and the brakes are applied. (TRB1)

Deadweight Tons: The lifting capacity of a ship expressed in long tons (2,240 lbs.), including cargo, commodities, and crew. (DOE5)

DEC: Drug Evaluation and Classification (NHTSA6)

Decision Height (DH): With respect to the operation of aircraft, means the height at which a decision must be made, during an Instrument Landing System (ILS) or Precision Approach Radar (PAR) instrument approach, to either continue the approach or to execute a missed approach. (14CFR1)

Deck Plate: A horizontal surface designed to provide a person with stable footing for the performance of work such as the connection and disconnection of air and electrical lines, gaining access to permanently-mounted equipment or machinery or for similar needs. (49CFR399)

Decoder: (See also Code; Discrete Code) The device used to decipher signals received from Air Traffic Control Radar Beacon System (ATCRBS) transponders to effect their display as select codes. (FAA4)

Dedicated Funds: Any funds raised specifically for transit purposes and which are dedicated at their source (e.g., sales taxes, gasoline taxes, and property taxes), rather than through an allocation from the pool of general funds. (FTA1)

Dedicated Tow: A single commodity moved from origin to destination by the same towboat without picking up or dropping off other barges. Often used in the movement of grain, coal, and bulk liquid. (TNDOT1)

Deep Sea Domestic Transportation of Freight: Establishments primarily engaged in operating vessels for transportation of freight on the deep seas between ports of the United States, the Panama Canal Zone, Puerto Rico, and United States island possessions or protectorates. (BOC1)

Deep Sea Transportation of Passengers: Establishments primarily engaged in operating vessels for the transportation of passengers on the deep seas except by ferry. (BOC1)

Defect Notification System: A computerized system that enables the Coast Guard to monitor the efforts of boat and equipment manufacturers in complying with 46 U.S.C. 4310. (USCG1)

Defense Visual Flight Rules (DVFR): Rules applicable to flights within an Air Defense Identification Zone conducted under the visual flight rules in Federal Aviation Regulation, Part 91. (FAA2) (FAA4) (FAA13)

Deferred Credits: Items for which additional information or events are required to determine their ultimate disposition and accounting classification, including deferred taxes, deferred investment tax credits, and other suspense items. (BTS4)

Deferred Income Taxes: Tax effects which are deferred for allocation to income tax expense of future periods. (BTS4)

Deferred Investment Tax Credits: Investment tax credits deferred for amortization over the service life of the related equipment. (BTS4)

Defined Mandatory Use Service Area: That listed in the determination of each Fleet Management Center or Fleet Management Subcenter. (GSA2)

Degree of (Critical) Hazard: A situation in which collision avoidance was due to chance rather than an act on the part of the pilot. Less than 100 feet of aircraft separation would be considered critical. (FAA10)

Degree of (No Hazard) Hazard: A situation in which direction and altitude would have made a midair collision improbable regardless of evasive action taken. (FAA10)

Degree of (Potential) Hazard: An incident which would have resulted in a collision if no action had been taken by either pilot. Closest proximity of less than 500 feet would usually be required in this case. (FAA10)

Delay: Delays are incurred when any action is taken by a controller that prevents an aircraft from proceeding normally to its destination for an interval of 15 minutes or more. This includes actions to delay departing, enroute, or arriving aircraft as well as actions taken to delay aircraft at departing airports due to conditions en route or at destination airports. (FAA3)

Delay Indefinite (Reason If Known) Expect Further Clearance (Time): Used by Air Traffic Control (ATC) to inform a pilot when an accurate estimate of the delay time and the reason for the delay cannot immediately be determined; (e.g., a disabled aircraft on the runway, terminal or center area saturation, weather below landing minimums, etc). (FAA4)

Delay Time: As applied to an automatic train stop or train control system, the time which elapses after the onboard apparatus detects a more restrictive indication until the brakes start to apply. (49CFR236)

Delay Time: The amount of time that the arrival must lose to cross the meter fix at the assigned meter fix time. This is the difference between Actual Calculated Landing Time (ACLT) and Vertex Time of Arrival (VTA). (FAA4)

Deliverability: Represents the number of future years during which a pipeline company can meet its annual requirements for its presently certificated delivery capacity from presently committed sources of supply. The availability of gas from these sources of supply shall be governed by the physical capabilities of these sources to deliver gas by the terms of existing gas-purchase contracts, and by limitations imposed by State or Federal regulatory agencies. (DOE5)

Delivered: The physical transfer of natural, synthetic, and/or supplemental gas from facilities operated by the responding company to facilities operated by others or to consumers. (DOE5)

Delivered Energy: The amount of energy delivered to the site (building); no adjustment is made for the fuels consumed to produce electricity or district sources. This is also referred to as net energy. (DOE5)

Demand Air Taxi: Use of an aircraft operating under Federal Aviation Regulations, part 135, passenger and cargo operations, including charter and excluding commuter air carrier. (FAA9)

Demand Response: Non-fixed-route service utilizing vans or buses with passengers boarding and alighting at pre-arranged times at any location within the system's service area. Also called "Dial-a-Ride." (APTA1)

Demand Response: Passenger cars, vans or Class C motor buses operating in response to calls from passengers or their agents to the transit operator, who then dispatches a vehicle to pick the passengers up and transport them to their destinations. A demand response operation is characterized by the following: 1) the vehicles do not operate over a fixed route or on a fixed schedule except, perhaps, on a temporary basis to satisfy a special need; and 2) typically, the vehicle may be dispatched to pick up several passengers at different pick-up points before taking them to their respective destinations and may even be interrupted en route to these destinations to pick up other passengers. (FTA1)

Demand Response: Personal transit service operated on roadways to provide service on demand. Vehicles are normally dispatched and used exclusively for this service. (FTA2)

Demand Responsive System: Any system of transporting individuals, including the provision of designated public transportation service by public entities and the provision of transportation service by private entities, including but not limited to specified public transportation service, which is not a fixed route system. (49CFR37)

DEMSTAT: Deployment / Employment / Mobilization Status System (MTMC1)

Demurrage: In domestic U.S. transportation, a penalty charge against shippers or consignees for delaying the carrier's equipment beyond the allowed free time provision of the tariff at the rail ramp ; in international transportation, a storage charge to shippers which starts accruing after a container is discharged from a vessel. The charge varies according to rules of the appropriate tariff. (MARAD2)

DEN: Stapleton International Airport (FAA11)

Department of Transportation (DOT): Establishes the nation's overall transportation policy. Under its umbrella there are ten administrations whose jurisdictions include highway planning, development and construction; urban mass transit; railroads; aviation; and the safety of waterways, ports, highways, and oil and gas pipelines. The Department of Transportation (DOT) was established by act of October 15, 1966, as amended (49 U.S.C. 102 and 102 note), "to assure the coordinated, effective administration of the transportation programs of the Federal Government" and to develop "national transportation policies and programs conducive to the provision of fast, safe, efficient, and convenient transportation at the lowest cost consistent therewith." (OFR1)

Departure Angle: The smallest angle, in a plane side view of an automobile, formed by the level surface on which the automobile is standing and a line tangent to the rear tire static loaded radius arc and touching the underside of the automobile rearward of the rear tire. (49CFR523)

Departure Center: The air route traffic control center having jurisdiction for the airspace that generates a flight to the impacted airport. (FAA4)

Departure Control: A function of an approach control facility providing air traffic control service for departing Instrument Flight Rules (IFR) and, under certain conditions, Visual Flight Rules (VFR) aircraft. (FAA4)

Departure Time: The time an aircraft becomes airborne. (FAA4)

Depreciation and Amortization: All depreciation and amortization expenses applicable to owned or leased property and equipment including that categorized as flight equipment or ground property and equipment. (BTS4)

Derailment: See also Accident, Casualty, Collision, Crash, Event, Fatality, Incident, Injury.

Derailment: A derailment occurs when one or more than one unit of rolling stock equipment leaves the rails during train operations for a cause other than collision, explosion, or fire. (FRA3)

Derailment/Bus Going Off Road: A non-collision incident which occurs as a result of rolling equipment leaving the rail, or buses leaving the roadway, and for roll overs. Report all incidents regardless of severity. (FTA1)

Derailment/Left Roadway: A non-collision incident in which a transit vehicle leaves the rails or road on which it travels. This also includes rollovers. Reports are made for all occurrences. (FTA2)

Deregulation: Revisions or complete elimination of economic regulations controlling transportation. For example, the Motor Carrier Act of 1980 and the Staggers Act of 1980 revised the economic controls over motor carriers and railroads. (MARAD1)

Descent Speed Adjustments: Speed deceleration calculations made to determine an accurate vertex time of arrival (VTA). These calculations start at the transition point and use arrival speed segments to the vertex. (FAA4)

Design Capacity: (See also Certified Capacity) Is the capacity associated with the direction of the flow observed on the peak day. (DOE1)

Design Head: The achieved river, pondage, or reservoir surface height (forebay elevation) that provides the water level to produce the full flow at the gate of the turbine in order to attain the manufacturer's installed nameplate rating for generation capacity. (DOE5)

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