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Train horns are audible warning devices found on most diesel and electric locomotives. Their primary purpose is to alert people of the presence of an approaching train, such as when nearing a grade crossing.

Among their secondary uses is for acknowledging signals given by railroad employees (i.e. during switching operations) in the absence of two-way radio communications.

Contents 1 History and background 2 Operation 2.1 Actuation 3 Train horns worldwide 3.1 North America 3.1.1 Manufacturers 3.1.1.1 Gustin Bacon Mfg. Co. 3.1.1.2 The American Strombos Co. 3.1.1.3 Westinghouse Air Brake Co. 3.1.1.4 The Leslie Co. 3.1.1.5 AirChime, Ltd. 3.1.1.6 Prime Manufacturing, Inc. 3.1.2 Audio samples 4 Common horn signals 4.1 United States 4.2 Germany 4.3 France 5 Location and placement 6 Train horns and popular culture 7 See also 8 Sources 9 External links 10 References

As diesel locomotives began to replace steam on most railroads, it was realized that the new locomotives were unable to efficiently utilize the steam whistles then in use.

Early internal combustion-powered rail vehicles were initially fitted with truck horns, but these were found to be unsuitable, and so the air horn design was scaled up and modified for railroad use.

Train horns are operated by compressed air, typically 125-140 psi (9-10 bar), and fed from a locomotive main air reservoir.

The basic operation of a train horn, or most any air horn for that matter, is that the air flow throughout the horn produces an action known as oscillation. Oscillation in a train horn is accomplished via a diaphragm enclosed within the power chamber. When air is applied to the horn, the diaphragm begins to vibrate against a nozzle. 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 creates "waves" of air, which in turn produce sound.

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

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

On North American locomotives built prior to the early 1990s, horns were actuated by a manual lever or pull-cord. This permitted use of a practice known to locomotive engineers as feathering, in that modulation of the horn was possible.

Many locomotives manufactured during the 1990s made use of pushbutton controls. In addition, several North American locomotives incorporated a sequencer pedal built into the cab floor beneath the operators position; that when depressed, sounded the grade crossing sequence.

Locomotives of European orgin have featured pushbutton control of air horns since the mid-1960s.

Current production locomotives from GE and EMD have utilized a lever-actuated solenoid.

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

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. 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 (known at the time as WABCO) was the first to offer airhorns specifically for railroad equipment, going as far back as the 1910s. Their model E2 was recognized by many for the deep, commanding tone it produced.

In response to the Leslie multi-note Chime-Tone series, Westinghouse offered a bracket to which three of their single-note "honkers" could be bolted onto, achieving the same result as what the Chime-Tones did for Leslie.

Overshadowed later on by Leslie and AirChime, WABCO eventually ceased production of horns for the North American market.

The Leslie Company 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 would later grace the rooftops of countless locomotives, such as the legendary Pennsylvania Railroad GG1, as well as thousands of EMD E and F-units. Leslie eventually introduced their own line of multi-note airhorns, known as the Chime-Tone series, in direct competition with AirChime.

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

Today, the company is known as Leslie Controls, Inc., and continues to manufacture SuperTyfon air horns for the railroad industry.

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 over routes 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 model H5. As the model designation indicates, this horn sounded a five-note, adjustable chord.

Over the years, AirChime had continued to perfect their horn design with the "M" (introduced 1950), "P" (1953), and "K" (1954) series, respectively. With the exception of the "K" series, most of the AirChime horns have been labelled as Nathan-AirChime - indicating their US licensee.

As of 2006, AirChime no longer markets locomotive horns, having sold this division of their business to Nathan Manufacturing, Inc.

Prime Manufacturing, Inc. had produced locomotive appliances for many years prior to their entry into the air horn market in the early 1970s. Their line of "Pneumatic Horns" was basically a derivative of the Leslie SuperTyfon design (Prime taking advantage of a patent expiration), though the Prime horns employed heavier castings than equivalents from Leslie, and sounded a somewhat richer timbre as a result.

Sales were brisk (railroads such as Union Pacific and the Burlington Northern were notable customers), but ultimately disappointing. Finding themselves increasingly unable to compete in a niche market dominated by Leslie and AirChime, Prime exited the air horn market in 1999.

The following are samples of selected air horns as used in North American railroad service. This is by no means a complete listing, as there are literally dozens of models and combinations thereof.

Audio files are in .WAV format:

• WABCO E2 (340kB)

• Leslie A200 (184kB)

• Leslie S3L (268kB)

• Leslie SL4T (197kB)

• Leslie S5T (392kB)

• Prime PM920 (434kB)

• Nathan M5 (194kB)

• Nathan P5 (255kB)

• AirChime K5H (221kB)

The meaning of horn signals varies from country to country. Most countries with large former or current state-owned railway networks, such as France, Germany or Great Britain, use standardized meanings of horn signals on their networks, whilst in other countries (for example, the United States) meanings of horn signals can vary between individual railroads.

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 at least 15 seconds, but not more than 20 seconds before entering a crossing. 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.

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 indications are updated to reflect modern practice.)

Those rules marked with an asterisk "*", must be sounded when and/or where applicable. Those signals without an asterisk convey information to employees, they must be used when voice communication is not available.

Rule		Sequence	Indication
14 (a)		o	Applying air brakes while standing.
14 (b)	*	– –	Proceeding. Releasing air brakes.
14 (f)	*	o o –	Acknowledging a flagman's stop signal.
14 (g)	*	o o	Acknowledging any signal not otherwise provided for.
14 (h)	*	o o o	Backing up.
14 (j)		o o o o	Calling for signals.
14 (l)	*	– – o –	1. Trains or engines approaching public highway grade crossings shall sound the horn for at least 15 seconds, but no more than 20 seconds before the lead engine enters the crossing. Trains or engines travelling at speeds greater than 45 mph shall begin sounding the horn at or about, but not more than, one-quarter mile (1,320 feet) in advance of the nearest public crossing. Even if the advance warning provided by the horn will be less than 15 seconds in duration. This signal is to be prolonged or repeated until the engine or train occupies the crossing; or, where multiple crossing are involved, until the last crossing is occupied. 2. Approaching tunnels, yards, or other points where railroad workers may be at work. 3. Passing standing trains.
14 (m)	*	o	Approaching passenger station.
14 (o)		o –	Inspect train for a leak in brake pipe system or for brakes sticking.
14 (p)	*	Succession of sounds	Warning to people and/or animals.
14 (q)	*	– o	When running against the current of traffic: 1. Approaching stations, curves, or other points where view may be obscured: and 2. Approaching passenger or freight trains and when passing freight trains.

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

Horn signals are regulated in the Zp category of the Eisenbahn-Bau- und Betriebsordnung. Their most common use today is when approaching a level crossing that lacks barriers, and for warning purposes.

Whistle posts are labelled with the letter "P" (for 'Pfeifen'). Common signals are:^[1]

Sequence	Meaning
_	Zp 1 - Generic "Attention" signal.
o	Zp 2 - Tighten handbrakes.
o o	Zp 3 - Strongly tighten handbrakes.
_ _	Zp 4 - Loosen handbrakes
ooo ooo ooo	Zp 5 - Emergency. Brake immediately.
_ o _	Zp 11 - Come. Used to call out for train staff.

Train horns are sounded where a whistle post (marked with the letter 'S' for 'siffler') is present. If the whistle post is labelled 'J' (meaning 'jour'), the horn is only to be sounded between 07:00 and 20:00. Horns must also be sounded when passing an oncoming train, shortly before reaching the last car of the train.

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

Air horns are no exception, and railroad mechanical forces mount these on locomotives where they are deemed most effective at projecting sound, and for ease of maintenance.

Below are a few images depicting the most common mounting applications:

Leslie model S5T air horn mounted atop the cab roof of a Seaboard System 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.	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 noise complaints from train crews, as well as discouraging theft. Unfortunately, acoustic performance suffers, and the sound is often muffled.
Typical horn mounting location on European locomotives.

Fitting a train horn to trucks or an SUV has become the current fad of many vehicle customizers^[2]. One should keep in mind that train horns are extremely powerful devices, and use of one while in motor vehicle traffic has the potential to 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^[3]. 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 immediate view on the vehicle in question.

Due to the encroachment of development, some suburban dwellers (known derisively as NIMBYs and CAVE People) have opposed railroad use of the air horn as a trackside warning device.^[4] 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, truck, or pedestrian, 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 ^[5].

• Train whistle

• CSXT Operating Rules (Effective October 1, 2007)

• 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.

• Nathan Manufacturing, Inc. - Offers air horns for both heavy and light rail applications.