"There isn't really a clear distinction
between some of the model names. A
"Road Switcher" (of any description) could
be used as a switcher or "transfer"
locomotive, as these are more of a function
than a "type". In general, you can apply the
following rules to help classify
locomotives:
Switchers - Usually (but not always)
this is considered to be a locomotive with
the cab located at, or near, the end of the
locomotive frame. These are also referred to
as "End Cab Switchers". There were also a
few earlier "switcher" models with the cab
located in the middle of the frame (like the
ALCo C415s and the "Center Cab" Baldwins).
As far as I know, all models of this type of
switcher on Class 1 railroads are out of
service. There are the exceptions of
some of the lighter weight GE and other
manufacturers industrial locomotives (like
the 44 tonner) that are in use as "plant
switchers" at various industries
and/or special purposes (I believe that UP
uses a 44 tonner in one of its tie plants).
The last of the EMD "End Cab" switchers
manufactured for Class 1
railroad service was the MP15 series. GE has
never produced an "End Cab" switcher
specifically for Class 1 service, although
many Class 1 railroads had
GE's 70 ton switchers, and GE cataloged an
"End Cab" switcher, called a U18BT, which it
never produced.
Cow/Calf Units - This is more of a "railfan"
term used to refer to a switcher-type
locomotive that has a "Cabless" booster
unit, usually of the same design
and horsepower, semi-permanently attached to
it. In some cases, this "semi-permanently"
attached booster was attached via a solid
drawbar instead of
the standard knuckle couplers. EMD produced
a series of locomotives called the "TR"
series which featured a "calf" units as a
part of the basic model. An
example of this is the TR6 model which was a
pair of SW8 switchers, one with a cab and
one without. It should also be noted that
the "calf" units have a
"control station" where the cab would
normally be placed. This "control station"
contained the engine/locomotive startup and
shutdown control in addition to various
gages for monitoring the engine (i.e. oil
pressure, coolant temperature, etc.).
Cab Units - This term is generally
used locomotives that are built with a
full-length car body that contains a place
for the crew to operate the locomotive
from and a control stand for that operation.
This term is usually used to refer to
locomotive of a similar design to EMD's "F"
and "E" unit series locomotives
(including the ALCo "FA"s, Baldwin "DL"s,
Fairbanks-Morse "C-Liners", etc.). Note that
in the construction of these locomotives,
the construction of the "Car Body" was an
integral part of the frame of the
locomotive. This is in contrast to
locomotives like the F40, F45s, and the
Canadian "Draper Taper" units, where the
"Car Body" is basically a non-structural
cowl that is lowered onto the basic
locomotive frame to cover the engine and
other inner components.
Booster Units - Generally used to
refer to the "Cabless" units associated with
the "Cab Units" above. These locomotives are
also referred to as "B" units. Like the
"calf" units above, there is a "control
station" for monitoring the
engine/locomotive *AND* there is what is
referred to as a "Hostler's Station". This
"Hostler's Station" has both a throttle and
an independent brake and is used to move the
"Booster Unit" or "B" unit using its own
power. This throttle is only capable of
moving the engine/locomotive at slow speeds
(generally only the equivalent of "Run 1")
and has to be "Cut In" and "Cut Out" by the
operator. This would also include the
various "B" units manufactured by EMD,
Baldwin, etc. such as the GP9B, GP30B,
SD24B, etc.
Cabless Units - As the name implies,
these units do not have a control cab. What
is interesting is that the term came into
"regular" (read: railfan) usage when the
Santa Fe and Burlington Northern started
rebuilding some of there SD40s (including
SD45-2 in the case of the Santa Fe) and
removed the cab. At about the same time, a
couple of other railroads (notably the
Southern Pacific) had either rebuild damaged
locomotives without a cab or were running
units that were awaiting new cabs from the
builders. As far as I know, only GE actually
produced brand new locomotives without cabs
and all of these were for the Burlington
Northern.
Before we go any further, let me say that
the term "Cabless" and "Booster" have been
used interchangeably throughout the years
and have even been combined as in "Cabless
Booster". Its one of those things that
you'll get a different answer based on
either who you talk to or whose book you're
reading. The "definitions" that I listed
above are what I've used over the years.
So why are there different terms for the
same basic locomotive type (like "Cabless"
verses "Booster"), and why there isn't a
"standard terminology" across
the board? The only answer that I can
provide you is that it is based when the
locomotive first appeared (time line) and
what it originally started out life
as. "Booster Units" were manufactured that
way by the various builders. "Cabless Units"
were generally rebuilt by the railroads (or
a contractor). In the case of some of the
very first "Booster Units" (such as EMCs "FT"s),
there wasn't any method provided for
starting the "Booster Units" engine unless
it was coupled to a "Cab Unit". In fact, all
of the "FT Booster Units" came from the
factory semi-permanently coupled (using a
drawbar) to a "Cab Unit", and only the "Cab
Units" contained batteries (used for
starting the engines in addition to other
things).
Road Switcher - basically, this is
any locomotive that isn't an "End Cab"
switcher or a "Cab Unit". They are
identified by having "running boards" along
the outside of the locomotive. It should be
noted that encompasses everything from the
GP7s and U25s to the SD90MACs and AC6000s
(and everything in between).
Slugs or TEBUs - "TEBU" stands for
"Tractive Effort Booster Unit". Slugs and
TEBUs are un-powered units (i.e. they do not
have an engine) that have traction motors
and additional weight added to them, which
when coupled to a properly-equipped
locomotive (sometimes referred to as a
"Mother Unit"), draw their "power" from the
engine/main generator of the attached
locomotive. Their purpose is to increase the
tractive effort of the locomotive consists
at slower speeds without adding another
locomotive. It also, generally, lowers the
"minimum Continuous Speed" rating of the
"Mother" locomotive to a level expectable
for the service, since the "Mother" unit is
supplying power for both itself and the
slug. In general, they are used in
slow-speed service and/or yard assignments,
generally not exceeding 20mph. It should
also be noted that not all slugs are created
equal. Some are meant for yard service only
(referred to as "yard slugs"), while others
are meant for slow speed "drag" service on
the mainline or branchlines (referred to as
"road slugs"). In addition to the slugs that
have been built by the various railroads,
both GE and Morrison-Knudsen built them. GE
called them "Mates", while Morrison-Knudsen
called them "TEBU"s. Some slugs can also act
as fuel tenders for the controlling
locomotive. Almost all slugs are equipped
with a blower motor to provide a source of
cooling for the traction motors. Slugs can
be of either 6 or 4 axle design.
Transfer Units - This is really more
a function of the "service" that the
locomotive may be involved in rather than a
specific locomotive type. In the
early days of dieselization, there were a
few specific models that were "Transfer
Units". At least, that is how they were
marketed. The TR6 model mentioned above was
one such unit, as was the ALCo T6 model. In
general, these specialized transfer
locomotives were basically switchers that
featured items such as road switcher trucks
(instead of switcher trucks), standardized
locomotive control stands, MU capability,
etc. Their primary use/service was to
transfer cars from one rail yard to another.
Brake Sleds - These are locomotives
that have been stripped of just about
everything (cab, engine, traction motors,
etc.) and weighted down, usually with
concrete. Their braking capabilities (i.e.
the brake shoes and associated brake
rigging) have been left intact and are
designed to work when the controlling
locomotive's independent brakes are applied,
thereby providing additional braking
capability. The controlling locomotives are
modified to provide a separate connection
for this purpose.
Now, before you take this too far, just know
that a lot of this is subject to change by
the various railroads and/or manufactures.
Union Pacific (and the Southern Pacific
before them), for example, uses what would
"normally" be classified as a "road
switcher" as a "switcher". These are SD38-2s
(2000
horsepower, 6 axle locomotives) which have
been modified for hump yard service by
changing both the traction motor gearing and
eliminating the locomotive's ability to
"transition" (i.e. change the electrical
system for the traction motors from serial
to parallel). Some of the earlier diesel
production,
especially from Baldwin and Fairbanks-Morse,
really confused things by offering the
option of different trucks underneath the
same basic machinery - The Baldwin AS615
(C-C, 6 powered axles), DRS-6-4-1500
(A-1-A/A-1-A, 4 powered axles with an
un-powered axle in between and powered
axles), and the DRS-4-4-1500 (B-B, 4 powered
axles) are basically the same model but with
different wheel/truck arrangements.
Now, if you like that, you'll love this.
Kansas City Southern (KCS) used to operate a
road slug that had been converted from an
old F7 car body. This slug
retained its cab and operating controls for
movements when the slug was the lead unit
and appeared to be an F7 from every angle
(except the front, which had a larger than
normal "buffer zone" around the front door
of the locomotive)! CSX has done similar
things with a few older GP35s (if I remember
correctly). They are identified by CSX as
RDMTs."
In a later posting, he corrected something
in the above article:
"Whoops...I neglected something in my
original post. I stated the following, which
was incorrect: "As far as I know, only GE
actually produced brand new locomotives
without cabs and all of these were for the
Burlington Northern."
Turns out that both EMD and MLW (Montreal
Locomotive Works) build "Cabless" locomotive
fairly recently. In the case of EMD, this
would be the GP60B (only the Santa Fe
ordered these, as far as I know), and MLW
built the M420B (BC Rail only?). GE's "Cabless"
model was a version of the B30-7 and was
referred to as a B30-7A. These were
originally built for the Burlington Northern
only, as far as I know (although I know of a
few that are currently "running around" on
other railroads and shortlines).
An interesting anomaly on the recent "Cabless/Booster"
front ... All of the recently, "as built"
units (i.e., those built by the
manufacturer) are of a B-B (4 axle, all
powered) design while the railroads, or
their contractors, have favored rebuilding
their own C-C (6 axle, all powered) units.
An "historical" note ... Both ALCo and EMD
built a couple of "Double Diesel", "Booster
Units". The EMD entry was the DD35B (also
referred to as a DD35) which was basically a
pair of GP35s on a common underframe that
rode on a pair of 4 axle, D-D, trucks (8
axles, all powered). Only the Union Pacific
and the Southern Pacific had these, and only
the UP had the similar "A" unit (cab and
controls) model the DD35A (also referred to
as a DDA35). This truck design later showed
up under Union Pacific's DD40AX (note: The
DD40 model is referred to by several
different names including "The Centennial",
DD40A, DD40-X, DDA40, DDA40-X, and the
DD40AX. A "B" unit was cataloged by EMD, the
DD40B, but never built). The ALCo entry was
one of their Century series, the C855. This
locomotive appeared as both a "Booster" unit
and a "Control Unit" and rode on 4 standard
B trucks, two under each end in a B+B-B+B
configuration (8 axles, 4 trucks, all
powered). Only the UP bought this
locomotive."
So now you know!!