Whistle Code is the "language" of train whistles that is used to communicate between trains or the train engineer to others. This language (in the United States) is set down by the A.A.R. (Association of American Railroads).

Many times, the codes will have a different meaning depending on context. In the listing, the following convention has been used: a 'o' refers to a short blast (a "toot" on the horn) while a "---" refers to a longer blast. The length of the line indicates the length of the blast compared to others.


---
Apply brakes (moving train approaching station stop)
Normal departure from station (stopped train starting up and leaving station)

--- ---
Release brakes (stationary train starting)
Raise Pantograph (electric locomotive only)

--- o ---
Lower Pantograph (electric locomotive only)

--- --- ---
Back up (when stationary) -- also seen as 'o o o'

--- --- o ------
Approaching public crossing (the signal beings some distance before the crossing and the long tail is held until the train engine is through. This signal may be repeated several times -- related to the next signal. This signal is the most recognized of all of the whistle codes)

------------
Approaching stations, junctions, or crossing
Recall flagmen
Material (not passenger) train ready to leave
Running (not stopping) through a station
Approaching a stop signal on
Detained at stop signal
Crossing a stop signal on after waiting

--- --- --- ---
Call to flagman to return from south or west

--- --- --- --- ---
Call to flagman to return from north or east

o o o o o o ...
Livestock or people seen on track ahead (more may be used)
Moving wrong way on double line
Danger!

--- o o
Next signal is important

o o
Answer to '--- o o'

o o o o
Call for signals (everyone tell who/what/where they are)
Request for signal to be repeated - signal not understood
Train cannot proceed - accident or failure
Protect train in rear

--- o
Running against traffic

o ---
Inspect train for leaks or bad brakes (to flagman)

--- o o o
Protect rear of train (to flagman)

o o o ---
Flagman protect ahead

--- --- o
Approaching meeting or waiting point

o --- o
Token not received or missed
Wrong authority to proceed
Passing stop signal at on with authority

------ o
Call for signal to be cleared (forget that)

This is all applicable only for North America where the A.A.R (Association of American Railroads) has created the standard. Other countries have different calls (if any are standard at all). In the UK, for example, the railways have been fenced off from non-rail traffic since the 1830s and thus was never an issue. Instead of whistles for communication between the engineer and the switchman, shutter and hand signals are used.


http://www.railwaystation.com/1942/06.html
http://www.cwrr.com/Lounge/Reference/rules/signals.html#5.8.2
http://irfca.org/faq/faq-signal5.html#whistle
http://www.catfish-hollow.com/faq.htm

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