Which Horns Do Union Pacific, BNSF, CSX & Norfolk Southern Use?

Which horns do Union Pacific, BNSF, CSX, and Norfolk Southern use? Today it is almost all Nathan AirChime K-series, but each railroad bought different models over the decades, and once you know which one is which, you can often name the railroad by ear before the train shows up.

The short answer: Nathan K-series on almost everything

Trains magazine’s 2021 explainer on locomotive horns says horns on new North American locomotives are built by Nathan Airchime and mostly come in three models:

New six-axle GE locomotives

Nathan K5HL

New six-axle Progress Rail locomotives

Nathan K5LLA

Siemens Charger passenger units

Nathan K5LA

That matters more than any single railroad’s preference. A brand-new GE-built unit on any of these four railroads probably left the factory with a K5HL unless the railroad later swapped it. The roof of a locomotive also changes over its life. Horns get replaced, swapped between units, and turned around, so treat every railroad list below as “what you’re most likely to hear,” not a fleet roster.

Leslie used to run the table. Wikipedia’s Leslie Controls entry puts it bluntly: “At one time, most trains used Leslie horns, but now Nathan has the majority of the market.” Its train-horn article captions the Leslie RS3L as “once the most common horn in use on North American railroads.” For the full story of that rivalry, read our Nathan vs Leslie comparison.

Why modern freight horns sound darker

If the newest freight horns sound more sour than the cheerful horns you remember, there’s a reason. Per Wikipedia’s Nathan Manufacturing entry, the federal horn rule of the mid-2000s set a maximum sound level for locomotive horns. In response, Nathan developed the K5LLA for EMD and the K5HL for GE.

The current rule, 49 CFR 229.129, requires a lead locomotive horn to produce between 96 and 110 dB(A) at 100 feet forward of the locomotive. Trains magazine adds that the test microphone sits 15 feet above the top of the rail.

Both newer horns add Nathan’s low 1L bell, which Wikipedia’s bell chart lists as middle C at about 262 Hz. The classic K5LA’s lowest note is the #1 bell, a D♯ at about 311 Hz.

Horn	Notes (per Wikipedia)	Chord	Where you hear it
K5LA	D♯, F♯, G♯, B, D♯	B major 6th	Amtrak, CSX, Norfolk Southern
K5HL (R2 arrangement)	C, D♯, F♯, A♯, C	C minor 7 flat 5	GE Evolution Series (“GEVO”) units
K5LLA (R1L arrangement)	C, D♯, F♯, G♯, B	Dissonant G♯ dominant 7th sharp 9	Mainly EMD SD70ACe
Leslie S-3L	C, D♯, A	No conventional name	Older freight power on many roads

The K5LA is a consonant major chord. The HL and LLA horns sit lower and clash on purpose. That low C rumble is the easiest single clue for spotting a newer freight unit.

Union Pacific: from Leslie S-3L to “HL” three-chimes

SoundTraxx’s horn-usage list, built as a sound guide for model railroaders, lists Union Pacific’s historical horns as the Leslie A200, Leslie A125, Leslie S3L, and Wabco E2. That is an all-Leslie-and-Wabco list with no Nathan at all.

The switch to Nathan is documented on Don Strack’s UtahRails.net history of UP locomotive features. It quotes a railfan email dated 02/02/2000: “UP used to have the Leslie S-3L on everything, but in recent years they have been buying the Nathan (AirChime) K-3HA.” The same email says that is what UP’s SD9043MAC units were delivered with. The writer also believed UP had announced a move to the K-3HA exclusively because of complaints about how its horns sounded. The writer blamed Leslies that “don’t stand up well to the abuse of button-controlled horn valves.” Treat that as one well-placed fan’s account, not an official UP statement.

Today Wikipedia’s Nathan entry lists the K3HL as “found on most UP AC6000/AC44” units. It also lists the K3LA as found on several Union Pacific locomotives, with the K-3LA-R2 bell-reversal arrangement common on UP. So on Union Pacific, three-chime horns are the norm, which sets UP apart from the five-chime-heavy eastern railroads.

UtahRails also explains a detail you can see from the platform. In the mid-1960s UP moved horns from the cab roof to above the radiator fans to keep ice and snow from freezing them. Studies in the early 1970s found the rear location masked the sound. After a 1974 change, horns went back toward the cab, and new SD40-2s switched over in March 1978.

BNSF: Santa Fe and Burlington Northern roots, GE K5HL today

BNSF inherited two horn traditions. SoundTraxx lists Santa Fe’s historical horns as the Nathan M5 and P3, Leslie A200, A125, S2M, and S3L, and the Wabco E2. Burlington Northern’s list includes the Nathan M3 and P3 plus Leslie A200, S2M, S3L, S5T, and RS5T. Wikipedia’s train-horn article adds a lesser-known name. Prime Manufacturing, which built horns derived from the Leslie SuperTyfon design, counted Union Pacific and Burlington Northern among its notable customers before it stopped making air horns around 1999.

For current power, the clearest evidence is a photo in Trains magazine’s horn explainer. It shows a Nathan K5HL on the roof of a new GE locomotive being built for BNSF at GE’s Fort Worth, Texas, plant. Wikipedia also lists the K3LA, including the K-3LA-R2 arrangement, as common on BNSF locomotives. If you hear a low, dark five-chime on a BNSF GE unit, a K5HL is the safe bet. A brighter three-note chord is more likely a K3LA.

CSX: the home of the K5LA

CSX is the easiest of the four to identify by ear. Per Wikipedia’s Nathan entry, the K5LA was first used by the Chessie System, one of CSX’s predecessors. It is now “the standard horn for Amtrak, CSX, Norfolk Southern, and Illinois Central.”

Wikipedia also describes the K-5LA-R24 as a common arrangement on CSX and Norfolk Southern locomotives. The 1, 3A, and 5 bells face forward and the 2 and 4A bells face backward. Trains magazine explains why freight horns are split this way: freight units often run in either direction, so railroads point some bells each way. Passenger units usually point all five forward.

The older layers still show up. SoundTraxx lists CSX’s historical horns as the Nathan P3, K5H, and K5LA plus the Leslie S3L and RS5T. Wikipedia notes the 1954-vintage K5H, with its haunting D♯ minor voicing, is still used on some older CSX engines. And because new six-axle GE units ship with the K5HL, a darker chord on a CSX GE unit is no surprise.

Norfolk Southern: K5LA, plus the P5

Norfolk Southern shares the K5LA with CSX, often in the same R24 reversed arrangement, per Wikipedia. What sets NS apart is the Nathan P5. Wikipedia’s Nathan entry calls Norfolk Southern “the most common user of this horn alongside the K5LA.”

The P5 has its own quirk. According to the same entry, Nathan revised the casting templates between 1976 and 1978 and the pitch of some bells changed. Pre-1978 “old cast” horns play the intended A major dominant 7th, and newer castings come out discordant. You can tell them apart by the casting marks: older bells read “Pat Pending” and newer ones read “Pat Pend.”

SoundTraxx’s list for Norfolk Southern Railway covers the Nathan M5, P3, P5, K5H, and K5LA plus the Leslie RS5T. Wikipedia also names NS among the users of the K5H. If you hear a bright five-chime with a slightly odd edge on NS, you may be hearing a new-cast P5 rather than a K5LA.

How to identify a railroad’s horn by ear

You don’t need perfect pitch, just a few listening habits.

• Count the notes. A thin three-note chord out West points to a UP or BNSF three-chime such as the K3HL or K3LA. A fuller five-note wash is the eastern K5LA or P5 sound.
• Listen for the low C. A growling bottom note below the familiar K5LA pitch means the 1L bell is in play, so it’s likely a K5HL or K5LLA on newer GE or EMD-lineage power.
• Bright and resolved, or sour? A happy, musical major-6th chord is the K5LA. A slightly off-key three-note cluster on an older unit may be a Leslie S-3L, whose C, D♯, and A, per LocomotiveHorns.info’s chord table, form no conventional chord.
• Mind the direction. On reversed horns, standing behind or beside the locomotive changes which bells you hear loudest, so the chord can sound different as the train passes. Our guide to why horn pitch drops as a train passes covers the other half of that effect.

The pattern tells you something too. Every crew, on every railroad, sounds two long, one short, and one long blast for a public grade crossing. Per 49 CFR 222.21, the signal generally starts at least 15 and no more than 20 seconds before the crossing. Our train horn signal guide decodes the rest.

Want that sound on your own truck?

Every horn in this article is a real locomotive part you can buy, usually refurbished. If you want the “CSX/Amtrak” sound, start with the K5LA, and if you’re torn between the three- and five-chime versions, our Nathan K3LA vs K5LA breakdown walks through chord, size, and air use. For the darker modern-freight growl, see our Nathan K5HL review and K5LLA review. Any of them needs serious air behind it, so read our used locomotive horn checklist before you bid.

Keep reading

• Nathan vs Leslie train horns: which locomotive horn sounds better?
• Nathan K3LA vs K5LA: which AirChime K-series sound fits you?
• Train horn signals and what they mean
• Locomotive horn rules: what 49 CFR 229.129 requires
• Nathan AirChime K5LA review

Sources

• Trains — Locomotive horns are important safety features (Chris Guss, 08/06/2021) — new locomotive horns built by Nathan Airchime; K5HL on new six-axle GE units, K5LLA on new six-axle Progress Rail units, K5LA on Siemens Chargers; forward/reverse bell arrangement on freight units vs all-forward on passenger units; 96–110 dB at 100 ft with the microphone 15 ft above the rail; photo of a K5HL on a new GE unit for BNSF at Fort Worth
• Wikipedia — Nathan Manufacturing — K5LLA for EMD and K5HL for GE after the mid-2000s FRA rule; K5LA, K5HL-R2, K5LLA-R1L notes and chords; K5LA first used by Chessie System and standard on Amtrak/CSX/NS/IC; K-5LA-R24 on NS and CSX; K5H on NS, CSX, BC Rail, C&NW; K3HL on most UP AC6000/AC44; K3LA and K-3LA-R2 on BNSF and UP; P5 on Norfolk Southern and the 1976–1978 casting change; bell chart (1L = C4, 262 Hz; 1 = D♯4, 311 Hz)
• SoundTraxx — Locomotive Airhorn Usage — historical horn lists for Union Pacific, Santa Fe, Burlington Northern, Burlington Northern Santa Fe, CSX, and Norfolk Southern Railway (“by no means a complete list”)
• UtahRails.net — External and Internal Features of UP Locomotives — 02/02/2000 email on UP’s move from the Leslie S-3L to the Nathan K-3HA, SD9043MAC delivery horns, and UP horn relocation history (1960s radiator mounting, 1974 change, March 1978 SD40-2 changeover)
• Wikipedia — Leslie Controls — “At one time, most trains used Leslie horns, but now Nathan has the majority of the market”
• Wikipedia — Train horn — Leslie RS3L “once the most common horn in use on North American railroads”; Prime Manufacturing’s Union Pacific and Burlington Northern sales and its exit from air horns around 1999
• LocomotiveHorns.info — Leslie SuperTyfon — S-3L bells 25, 31, 44 sounding C, D♯, A, with no conventional chord name
• Cornell LII — 49 CFR 229.129 — 96 to 110 dB(A) at 100 ft requirement for lead locomotive horns
• Cornell LII — 49 CFR 222.21 — two long, one short, one long crossing pattern; sounding begins 15 to 20 seconds before the crossing