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D: Depth (slab thickness) (FHWA19)

D&H: Dangerous and Hazardous (MARAD2)

D-ATIS: Digital - Automatic Terminal Information Service (FAA20)

D-factor: Peak directional volume (as percent DHV) (FHWA19)

D/B: Design/Build (FTA5)

D/B/B: Design/Bid/Build (FTA5)

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 Orleans, LA) (USCG5)

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

DA: Descent Advisor (FAA17)

DA: Decision Altitude/Decision Height (FAA20)

DA: Direct Access (FAA20)

DA: Division Administrator (FHWA18)

DA/H: Decision Altitude/Height (FAA20)

DAB: Dial-A-Bus (TRB1)

DABBS: DITCO Automated Bulletin Board System (FAA20)

DACS: Digital Aeronautical Chart Supplement (FAA20)

DADS: Digital Aeronautical Database System (FAA20)

DADSS: Driver Alcohol Detection System for Safety (NHTSA7)

DAFIS: Departmental Accounting and Financial Information System (FAA20)

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 (FAA20)

DAL: Dallas Love Field (FAA11)

DALR: Digital Audio Legal Recorder (FAA20)

DALY: Disability-Adjusted Life-Year (NHTSA7)

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: Designated Agency Representative (FAA20)

DAR: Defense Access Road Program (FHWA16)

DAR: Dial-A-Ride (TRB1)

DARC: Direct Access Radar Channel (FAA19)

DARP: Dynamic Aircraft Route Planning (FAA20)

DART: Dallas Area Rapid Transit (FHWAII)

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

DASI: Digital Altimeter Setting Indicator (FAA19)

DASR: Digital Airport Surveillance Radar (FAA20)

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

DAY: James M Cox Dayton International Airport (FAA11)

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

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

dB: Decibels (BTS11)

DB: Database (FAA20)

DB: Decibel (FAA20)

DBA: Decibels (BTS10)

DBA: Database Administrator (FAA20)

dBA: Decibels A-weighted (FAA20)

DBCRC: Defense Base Closure and Realignment Commission (FAA20)

DBE: Disadvantaged Business Enterprise (FTA5)

DBIA: Design Build Institute of America (FTA5)

DBMS: Data Base Management System (FAA20)

DBN: Day Beacon (USCG5)

DBOM: Design Build Operate Maintain (FTA5)

DBRITE: Digital Bright Radar Indicator Tower Equipment (FAA20)

DC: Direct Current (BTS10)

DCA: Washington National Airport (FAA11)

DCA: Defense Communications Agency (FAA20)

DCAA: Dual Call, Automatic Answer Device (FAA20)

DCC: Display Channel Complex (FAA19)

DCC: Direct Channel Complex (FAA20)

DCCU: Data Communications Control Unit (FAA20)

DCE: Data Communications Equipment (FAA20)

DCM: Dangerous Cargo Manifest (RSPA1)

DDA: Dedicated Digital Access (FAA20)

DDACTS: Data-Driven Approaches to Crime and Traffic Safety (NHTSA7)

DDD: Direct Distance Dialing (FAA20)

DDHV: Directional DHV, vph (FHWA19)

DDM: Difference in Depth of Modulation (FAA20)

DDP: Designated Driver Program (NHTSA7)

DDPS: Dual Driver Protective Service (MTMC1)

DDS: Digital Data Service (FAA20)

DDT: Deflagration-To-Detonation Transition (RSPA1)

DEA: Drug Enforcement Agency (FAA20)

DEACON: Drug Enforcement Assistance and Coordination (FHWA18)

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 Tonnage (Water): The carrying capacity of a vessel in long tons (2,240 pounds). It is the difference between the number of tons of water a vessel displaces light and the number of tons it displaces when submerged to the load line. (BTS11)

Deadweight Tons: The number of tons of 2,240 pounds that a vessel can transport of cargo, stores, and bunker fuel. It is the difference between the number of tons of water a vessel displaces 'light' and the number of tons it displaces when submerged to the 'load line.' (BTS12)

DEAL: Design Equivalent Axle Load (FHWA19)

DEC: Drug Evaluation and Classification (NHTSA6)


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