What is the chord for a train whistle?

Answer 1

A car horn is usually F.

I got the following from Google Wikipedia.

American train whistles usually had anywhere from one to six frequencies which were sounded together. As compared with automobile horns, for example, which form a major third, usually with the notes "F" and "A", the train whistle usually forms a non-major chord which is full of dissonance, allowing it to have a distinct, frightening, and serious sound, rather than a happy one.

A train whistle is usually low in pitch, compared to similar mobile signaling devices on automobiles, trucks, bicycles, etc. The low pitch helps people mentally connect with the fact that the source of the sound is large in size and weight.

Answer 2

Train Whistle Chord

Answer 3

The trains that run near my house usually play a major 6 chord. So in a Cmaj6 chord, the notes are C, E, G and A. The third (E) is usually much flatter than you might hear on a piano. Thanks for the fun question.