- Dark Signal: A block signal that is displaying no discernible aspect, often due to burned out lamps or local power failure. Most railroads require that a dark signal be treated as displaying its most restrictive aspect, e.g., stop and stay for an absolute signal.
- Dark territory: A section of track without block signals.
- Dead in tow: The movement of a locomotive as part of a freight train, on its own wheels but not under its own power.
- Dead man's handle or Dead man's switch: A safety mechanism on a train controller which automatically applies the brake if a lever is released. It is intended to stop a train if the driver is incapacitated. In some forms, this device may be pedal-actuated.
See also: Dead-man's vigilance device
- Deadhead: (US) 1. A nonrevenue (i.e., nonpaying) passenger. 2. The nonrevenue movement of locomotives and/or cars.
- Decapod: A steam locomotive with a 2-10-0 wheel arrangement.
- Defect detector: A track side device used to detect various defects such as hotboxes (overheated axle bearings), dragging equipment, leaning cars, overloaded cars, overheight cars, seized (locked) wheels, etc.
- Demurrage: A monetary charge levied by a railroad to a customer for excessive delay in loading or unloading cars.
- Derail: A safety device that will derail vehicles passing it, often used to prevent rolling stock from unintentionally fouling the mainline. Sometimes incorrectly called a "derailer".
- Detonator: Small explosive charges placed on the running rail which detonate when run over; used to warn drivers in following trains of an incident ahead. Also called track torpedoes (US).
- Diamond: Track which allows a rail line to cross another at grade.
- Diesel multiple unit or DMU: A set of diesel-powered self-propelling passenger rail vehicles able to operate in multiple with other such sets. Such units, especially those consisting of a single vehicle, are sometimes termed railcars.
- Direct Traffic Control (DTC): A system in which train dispatchers communicate directly with train crews via radio to authorize track occupancy in predefined blocks.
- Distributed power: A practice employed to move large trains through the mountains. Consists of the locomotives on the head end, a "swing" (mid-train) helper or two, and pusher locomotive(s) on the rear; today, all units are remotely controlled by the engineer in the lead unit. The power distribution alleviates stress on the couplers and relieves the lead units of the full weight of the train, making it easier to move on grades.
- Ditch lights: A pair of lights, usually found on modern locomotives, located several feet below and outboard of the main headlight, that may alternately flash when the train is sounding its horn.
- DOO: Driver-only operation, also referred to as One person train operation (OPTO).
- Doodlebug: Gasoline-electric self-powered passenger car used for small capacity rural commuter service. Also a British Rail Class 153 DMU.
- Double, as in "Double the hill": if a train has insufficient power to climb a grade and no helpers are available, the train will be split into two sections and run separately to the top.
- Double iron (slang, US): A double-tracked main line.
- Doubleheading or Doubleheader (US): In which two steam locomotives are coupled head-to-tail in order to haul a heavy train up a long and/or steep hill. In the present day, doubleheaders (and occasionally tripleheaders) are done primarily on large passenger trains or as a show for railfans.
- Down: (UK) A direction (usually away from London, other capital city, or the headquarters of the railway concerned) or side (on left-running railways, the left side when facing in the down direction). The opposite of up. The down direction is usually associated with odd-numbered trains and signals. In Australia it is used relative to the state's capital city. US railways use the compass points northbound, southbound, eastbound and westbound.
- Drag: A long, heavy freight train moving at low speed.
- Dragging equipment detector: See Defect detector
- Drawbar: 1. The part of a coupler that attaches to the frame of the car or locomotive; may be equipped with a pneumatic cushion depending on a freight car's design cargo, e.g. an autorack. 2. The pinned double bars coupling a steam locomotive to its tender.
- Drift: Cutting off power and allowing a train to coast.
- Driver (UK), Engineer (US): The operator of a railway/railroad locomotive.
- Driver: A wheel in contact with the rail that also propels a locomotive.
- Driving Van Trailer or DVT (UK): A class of control cars used in the UK. (See also: DBSO - predecessor to the DVT)
- DSLE (US): abbr. Designated Supervisor of Locomotive Engineers.
- Dwarf signal: A signal light that is considerably smaller and closer to the ground than a high-mast signal; often absolute, and placed within interlocking limits, its aspects tend to differ from those conveyed by a taller signal for certain indications. Also called 'pot' or 'jack'.
- Dynamic braking: The use of a diesel locomotive's electrical output to maintain or retard train speed on a descending grade, without relying solely on the air brakes.
- Dynamite (slang, US): To make an emergency brake application; also "plug" and "shoot".
|
.
|