Railroading Glossary
The following glossary is arranged alphabetically with each term catalogued by first letter. Select a letter below to begin.
A | B | C | D | E | F | G | H | I | J | K | L | M
N | O | P | Q | R | S | T | U | V | W | X | Y | Z
D&H
Abbreviation for Delaware & Hudson Railroad.
Dash 2
In 1972 Electro-Motive Division changed the electrical systems in its locomotives. The change wasn't enough to warrant new model designations, so EMD appended a "-2" to existing model designation. EMD "-2" engine models were produced from 1972 to 1987 and included the following features: 645 engine, modular electronics, and, later, improved wheel-slip control, but without microprocessors.
Dash 7
In 1977 General Electric made a number of internal changes to its locomotives and changed the model designations from the U series to the Dash 7 series-U23B was succeeded by B23-7 and U30C by C30-7, for example. The "7" was supposed to indicate the year of introduction.
Dash 8
Nomenclature for referring to GE models introduced in 1983 that contained several evolutionary internal changes, including: microprocessor to control engine and electrical functions, new hood and cab design, improved wheel-slip control system.
Deadhead
To move in a train, not to support its operation, but to be properly positioned for later work. Can apply to railroad employees as well as equipment.
Decapod
A 2-10-0 steam locomotive (2-wheeled pilot truck, 10 driving wheels, no trailing truck).
Degree
A measure of the sharpness of a curve. It is the angle through which the track turns in 100 feet of track. The number of degrees is equal to 5,729 divided by the radius of the curve in feet.
Demurrage charges
Fees assessed by a railroad to a customer who does not load or unload a freight car within a specified period of time.
Departure yard
Yard where cuts of cars are assembled to form outbound trains.
Derail
(verb) to leave the rails; (noun) a safety device placed on the track, usually on a siding, that guides a rolling car off the rails to prevent it from continuing onto the main line and possibly causing a collision.
Derating
Any of several changes made to a diesel engine to improve fuel efficiency or lower maintenance costs, including removal of a turbocharger and adjustment of fuel settings. The usual result is a nominal horsepower rating for the engine.
Derrick
Specially designed rail-mounted crane, often with two hoists, intended to lift and drag locomotives or cars and clear debris from the roadbed.
Designated operator
A company or organization designated by a state regulatory agency to operate the property of a railroad. The term is customarily used in connection with lines cast off by Conrail.
Diamond
The crossing of two railroad tracks at grade without a bridge. Named for the diamond shape of the center section of the intersecting rails if the lines cross at other than 90 degrees, which is often the case.
Diesel-electric locomotive
Locomotives with a large diesel engine, or prime mover, which turns an alternator to produce electricity. The electricity is then fed to axle-mounted electric traction motors that turn the wheels.
Directed Service Order
An order issued by the Interstate Commerce Commission directing one railroad to handle the traffic of another, if the second was unable to by reason of strike, damage, abandonment, or other emergency.
Direction of Traffic rules
Operating rules employed in double-track, automatic block signal territory, where each track is signaled for movement in one direction only.
Displacement
The volume displaced by a complete stroke of the piston. It is the product of the cylinder area and the piston stroke.
Distillate
A petroleum product that gained favor in the late 1920's because of its low cost relative to gasoline.
Distributed Power Unit (DPU)
An unmanned locomotive, controlled remotely from the lead cab, and placed in the middle or at the rear of the train.
Dodger
A local train that must "dodge" out of the way of through trains.
Dog-catch crew
Train operating personnel sent to relieve a crew that has reached its maximum legal time on duty, at a point short of the train's intended destination.
Doghouse
Nickname for a shelter placed on the tender deck of steam locomotives to house the head brakeman.
Doodlebug
One of several nicknames for self-propelled passenger-carrying rail cars built in the early 1900's. They were powered by gasoline engines (later diesel engines), which turned an electric generator which fed current to traction motors geared to the wheels. Most were built in the 1910's and 1920's; the last ones were removed from service around 1960. Also called "motor cars" and "puddle jumpers".
Double the hill
To move a train up a grade in two halves, because the locomotives have insufficient power to move the entire train up at once.
Doubleheading
The use of two locomotives with two separate crews to pull a train.
Double-stack
The transportation of containers stacked two high on special cars.
DPU
Distributed Power Unit. An unmanned locomotive, controlled remotely from the lead cab, and placed in the middle or at the rear of the train.
Drag
Slang term for a slow freight.
Dragging equipment detector (DED)
Electronic sensor placed between and alongside the rails that monitors passing trains and warns of unsafe conditions, such as objects dragging below or alongside the cars.
Drawbar force
Total tractive effort minus the tractive effort needed to move the locomotive.
Drayage
Movement by truck
Drone
See Slug.
DT&I
Detroit, Toledo & Ironton Railroad.
DTC territory
Portion of a line operated by Direct Traffic Control, under which the dispatcher authorizes trains to proceed in one or more blocks, whose boundaries are pre-set.
Dual control switch
Track switch that can be operated remotely by a dispatcher or hand-thrown.
Dual-mode
A locomotive capable of operating as a diesel-electric or as a "straight" electric by drawing power from an outside source.
Dual-service
Used to describe a locomotive designed to pull both freight and passenger trains.
Dump the air
Make an emergency application of the air brakes.
Duplex-drive
A non-articulated steam locomotive with two sets of cylinders and drive wheels.
Dwarf signal
Short signal, often placed between tracks.
Dynamic braking
Originally called regenerative braking when applied to electrical locomotives. It is a system for temporarily employing traction motors as generators and using the resulting electromotive force to retard the train. On some electric railroads the current produced is returned to the power distribution system. On diesels the current produced by the traction motors is passed through resistors that convert the energy to heat, which is in turn dissipated into the air by fans.
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