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Here's the current FRA rule, I don't know whether it's a lower db level than previously required or not.

Title 49: Transportation
Subpart C—Safety Requirements


§ 229.129 Locomotive horn.

(a) Each lead locomotive shall be equipped with a locomotive horn that produces a minimum sound level of 96 dB(A) and a maximum sound level of 110 dB(A) at 100 feet forward of the locomotive in its direction of travel. The locomotive horn shall be arranged so that it can be conveniently operated from the engineer's usual position during operation of the locomotive.
Thank you, Ed.

Youqing (wife) and I both noticed that some locomotive horns seem less loud than before.
They seem to be on the newer locomotives.
^ Yes. Lower frequencies travel farther through air and penetrate vehicles better.

I wish that my Federal Signal 2t22A, now an active tornado siren, had 5 and 6 openings in the stators instead of 10 and 12 ports.
It would then sound an octave lower. (At 3,750 rpm, notes D4 and F4 instead of D5 and F5.)

(Even better would be 4 and 5 ports. But they would produce a perfect 4th musical interval instead of the 2t22's perfect minor third.)
Due to the Doppler effect, a horn will sound much different when the engine is moving slowly than when it is moving fast.
I have recorded train sounds for almost 50 years and I can tell you the horns of today are just as loud. There are many varying factors to how they sound to us. Cold air, hot air, humidity, wind direction, physical condition of the horn and that includes what kind of valve operates the horn, air pressure, etc. The horn on a UP U50 was sometimes almost drowned out by the engine noise. The other day while standing trackside I had to put my finger in ear as the train passed. Steam whistles are really loud too. Still nothing like a distant horn or whistle in the middle of the night to start the adrenaline. Wait I think I hear one calling now. is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to - An online railroad bookstore featuring a curated selection of new and used railroad books. Railroad pictorials, railroad history, steam locomotives, passenger trains, modern railroading. Hundreds of titles available, most at discount prices! We also have a video and children's book section. - An online model railroad bookstore featuring a curated selection of new and used books. Layout design, track plans, scenery and structure building, wiring, DCC, Tinplate, Toy Trains, Price Guides and more.

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