A Morse code-like system governs when and how train engineers sound their horns

Some people who live near train tracks don’t need an alarm. The loudly elongated wooo that reverberates through their windows every morning gets the job done.

Intrigued by the meaning behind the horn, one Bryn Mawr resident reached out to Curious Philly, The Inquirer’s forum for questions about the city and region, wondering: Do train engineers have guidance for when to sound the horn? Is there a stated protocol for how long they should do so? Is there a “too early” or a “too late” time of day? The reader speculated the engineer could be “giving an audio wave to a friend, or waking up his kid for school.”

Turns out, the train isn’t waking up anyone on purpose. Instead, it’s communicating with others. It’s like a version of Morse code for trains.

Every engine whistle, horn signal, or combination of the two, has a meaning dictated by the Northeast Operating Rules Advisory Committee. This commission establishes operating rules for railroads in North America; rule 19 in particular regulates the horn usage.

Rules don’t state how long the operator must blow the horn. However, each sound must be different in intensity and duration to make sure the right message is conveyed.

These auditory signals are illustrated in the rule book by o’s and lines. An “o” represents a short sound and a “—” a long one.

A single long wooo is a “—” signal and alerts the crew to apply brakes. Three short horns would be seen as “o o o,” meaning that when stopped, the train has to back up.

There are more complex instructions, such as two long wooos followed by a short one and another long one. This is used when approaching a public highway-rail crossing at grade and with specific signage, and it comes with many instructions.

Using the horn in an unnecessary way is prohibited. Yet, there might be some sounds not shown in the rule that don’t indicate a misuse.

Amtrak and SEPTA have additional instructions.

A SEPTA spokesperson was not able to give specifics, but said they “have to do with overall standard safety procedures and technicalities.”

Trains don’t adhere to the 9-to-5 hustle.

Certain horn whistles might not be required after reasonable hours, but others “are required whenever a particular condition is met. And that condition could happen at any time, day or night,” the SEPTA spokesperson said.

For example, whenever there are road workers on or near the track, the engineer must sound a few short horns, typically two to four.

Bryn Mawr residents in particular might be hearing this a lot these days because Amtrak is upgrading that substation, so workers can be present throughout the day.

Regardless of the message, whistle rules are in place for everyone’s safety.

“Anyone in the area of a train or train tracks should always remember that trains can come at any time, on any track, and from any direction, so diligent caution is key,” the spokesperson said.