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Train horns are audible warning devices found on most diesel and electric locomotives. They most commonly are used for internal communication between train staff, i.e. during shunting operations, and for warning purposes to members of the public who are near on on the rail line, for example on a level crossing.

History and background

As diesel locomotives began to replace steam on many railroads, it was realized that the new locomotives were unable to utilize the steam whistles then in use. Early internal-combustion locomotives were initially fitted with truck horns, but these were found to be unsuitable, and so the air horn design was modified for railroad use.

Operation

Classic train horns are operated by compressed air, typically 130-145 psi (9-10 bar), and fed from a locomotive main air reservoir. On American locomotives built prior to the early 1990s, they are actuated by a manual lever or pull-cord. Current American locomotives, as well as European models built since the mid-1960s, make use of pushbutton controls.

The basic operation of a train horn, or most any air horn for that matter, is that the air flow throughout the horn causes oscillation, producing sound waves. Oscillation in a train horn is accomplished via a diaphragm. When air is applied to the horn, the diaphragm begins to vibrate. Since the position of the diaphragm at any given moment during the vibration will allow more or less air through the horn, the constant oscillation of the diaphragm causes "waves" of air which in turn produce audible sound.

The configuration and dimensions of the bell ("bell" being the correct term for the trumpet assembly) determine the frequency produced (measured in Hz), and hence, the fundamental.

Many early three and five-note train horns were designed to play basic musical chords.

Manufacturers

North America

There have been six major manufacturers of air horns for railroad use in North America. Of these, only Airchime, Ltd. and Leslie Controls, Inc. remain today.

Gustin Bacon Mfg. Co.

The Gustin Bacon Mfg. Co. of Kansas City, MO offered airhorns for use on railroad equipment prior to the Second World War.

The American Strombos Co.

The American Strombos Co. of Philadelphia, PA (later to become known as Buell) sold modified truck horns for rail use. They were often installed on small locomotives and railcars (for example the Doodlebugs).

Westinghouse Air Brake Co.

Westinghouse (under their WABCO subsidiary) was the first to offer airhorns specifically for railroad equipment, going as far back as the 1910s. Their model E2 was known by many for the deep, commanding tone it produced. Overshadowed later on by their post-WWII competitors, WABCO no longer produces horns for the North American market.

Leslie Controls, Inc.

Leslie Controls originally began horn production by obtaining the rights to manufacture the Kockums Mekaniska Verkstad line of Tyfon brand airhorns, marketing these for railroad use in the early 1930s. Their model A200 series graced the rooftops of countless locomotives, such as the legendary Pennsylvania Railroad GG1, as well as thousands of EMD E and F-units. Leslie would later introduce their own line of multi-note airhorns, known as the Chime-Tone series, in direct competition with Nathan-AirChime.

Poor sales of the Chime-Tones (due to the added weight of the assembled horn, as well as requiring an ample air supply) led the Leslie Co. to develop the SuperTyfon line of horns utilizing interchangeable parts. Horns were offered in single, dual, triple, quad (in the case of Amtrak's SDP40F locomotives), and five note variants. Until recently, SuperTyfon products were the mainstay of almost all railroad motive power in the United States.

Nathan-AirChime, Ltd.

Nathan-AirChime, Ltd. got their start in train horn production through the work of Robert Swanson in 1949. Prior to the early 1950s, locomotives were equipped with airhorns that sounded but a single note.

Swanson set out to change this by developing a horn which could almost mimic the sound of a classic steam whistle. Using ancient Chinese musical theory, Swanson produced the six-note model H6. However pleasant the horn may have sounded, this was impractical for railroad use due to its relatively large size and weight. It should be noted that since railroad equipment operates in areas restricted by physical clearance, the difference of only a few inches may prohibit that equipment from operating on the line in question. Swanson would later refine the design into the H5. As the model number indicates, this horn sounded a five-note, adjustable chord.

Nathan-AirChime has since gone on to perfect their horn design with the M (1950), P (1953), and K (1954) series, respectively.

Prime Manufacturing, Inc.

Prime Manufacturing, Inc. had produced locomotive appliances for many years prior to their entry into the horn market in the early 1970s. Basically a derivative of the Leslie SuperTyfon design (due to a Leslie patent expiration), though the Prime versions employed heavier castings and sounded a somewhat richer tone as a result. Sales were brisk (Union Pacific was a notable customer), and unable to compete with offerings from Leslie and AirChime, as well as ever-stringent government regulation, Prime left the horn market in 1999.

Location and placement

As many people do with their personal vehicles, railroads order locomotives with many different options in order to suit their operating and maintenance practices.

Horns are no exception, and railroad mechanical forces mount these on locomotives where they are deemed most effective at projecting sound. Below are a few images depicting the most common mounting locations:

• Leslie model S3L air horn mounted atop the cab roof of a Santa Fe locomotive in the classic location. Leslie model S3L air horn mounted atop the cab roof of a Santa Fe locomotive in the classic location.
• On many locomotives with high short hoods, such as this Norfolk Southern GP38-2, the air horn can be located away from the operating cab. On many locomotives with high short hoods, such as this Norfolk Southern GP38-2, the air horn can be located away from the operating cab.
• AirChime model K5H mounted on a custom bracket. Not only is the horn located here, but the air-operated bell as well. AirChime model K5H mounted on a custom bracket. Not only is the horn located here, but the air-operated bell as well.
• On newer locomotives, the horn is mounted atop the engine compartment due to complaints from train crews. However, acoustic performance suffers, and the sound is often muffled. On newer locomotives, the horn is mounted atop the engine compartment due to complaints from train crews. However, acoustic performance suffers, and the sound is often muffled.

Common Horn Signals

Railroads are required by a variety of state and federal laws to sound horns in advance of all crossings. Horns are sounded for safety reasons, namely, to warn of approaching trains. (See also Train whistle (Whistle code) for traditional horn and whistle signals.)

The following are the required horn signals listed in the operating rules of most North American railroads, along with their meanings. Signals are illustrated by an "o" for short sounds, and "-" for longer sounds. (Note that these signals and their meanings are updated to reflect modern practice.)

Exception: Engine horn signals required by rules 14 (b) and 14 (h) do not apply after momentary stops in continuous switching movements.

Government ruling on the use of train horns

On April 27, 2005, the Federal Railroad Administration (FRA), which enforces rail safety regulations, published the final rule on the use of locomotive horns at highway-rail grade crossings. Effective June 24, 2005, the rule requires that locomotive horns be sounded at all public grade crossings 15-20 seconds before entering a crossing, but not more than one-quarter mile (400 m) in advance. This rule applies when the train speed is below 45 mph (70 km/h). At 45 mph or above, trains are still required to sound their horn at the designated location (usually marked with a whistle post).

The pattern for blowing the horn remains two long, one short, and one long. This is to be repeated as necessary until the lead locomotive fully occupies the crossing. Locomotive engineers retain the authority to vary this pattern as necessary for crossings in close proximity, and will be allowed to sound the horn in emergency situations no matter where the location.

A ban on sounding locomotive horns in Florida was ordered removed by the FRA after it was shown that the accident rate doubled during the ban. The new ruling preempts any state or local laws regarding the use of the train horn at public crossings. This also provides public authorities the option to maintain and/or establish quiet zones provided certain supplemental or alternative safety measures are in place, and the crossing accident rate meets government standards.

Train horns and popular culture

Fitting a train horn to trucks or an SUV has become the current fad of many vehicle customizers. One should keep in mind that train horns are extremely powerful devices, and use of one while in motor vehicle traffic can cause an accident. They may also violate local noise ordinances. Recent years have seen an increase of horn theft from railroad property, it is believed that the great majority of these crimes are perpetuated for the benefit of vehicle customizers and truckers.

On the other hand, there are those who collect train horns for their rarity and nostalgic value. Such items can command high prices among collectors. One rule of thumb may be that if the horn(s) are mounted prominently on the vehicle, the owner is a responsible collector, whilst those of the faddish vehicle customizer are generally hidden from view on the vehicle in question.

Due to the encroachment of development, some suburban dwellers (known derisively as NIMBYs and CAVE People) have opposed the railroad use of the air horn as a trackside warning device. This despite the fact that in most locations, the railroad had been established long before the development sprang up.

Residents in some communities have attempted to establish quiet zones, in which train crews are instructed not to sound their horns, except in case of emergency. Given the speed at which many trains travel, as well as the disparity in mass between railroad equipment and an automobile or truck, incidents often occur without warning. The effects of a train colliding with an errant automobile have been likened to that same automobile striking an empty soda can.

External links

• Federal Railroad Administration - Complete text on the ruling concerning the use of locomotive horns at highway-rail grade crossings.

• Five Chime Consultants - The original online spotters guide to diesel locomotive horns as used throughout the United States and Canada. Fully illustrated, with audio samples and background information on each horn.

• Trainhorns.net - Collectors guide to locomotive horns. Includes information on identifying rare makes and models, restoration, and maintenance.

• Leslie Controls, Inc. - Makers of SuperTyfon brand air horns for rail, marine, and industrial use.

• AirChime Manufacturing Co. Ltd. - Offers air horns and whistles for both heavy and light rail applications.

Audio samples

The following audio files are in .WAV format:

• WABCO E2 (306kB)

• Leslie A200 (256kB)

• Leslie S3L (340kB)

• Leslie SL4T (197kB)

• Leslie S5T (209kB)

• Prime PM920 (174kB)

• Nathan M5 (194kB)

• Nathan P5 (255kB)

• Nathan K5H (221kB)

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• Articles lacking sources from February 2007
• Locomotive parts
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