Quite simply put, the
song to be sung whenever the occasion of going through a
tunnel arises, especially if the tunnel in question is going beneath some body of water tens of thousands of tons above. The tune is arbitrary (sometimes monotonous, though if you can get the other vehicle passengers to join in, the resultant impromptu harmonies can be interesting enough to get your minds off your impending doom) and the words are quite easy to remember:
and a-one, and a-two, and a-one, two, three, four:
Oh, we're all going to die!
We're all going to die!
We're all going to die!
We're all going to die...
The song (best timed to coincide four flashes of that eerie yellow tunnel-light per line) is to be sung until there is once again blue sky visible overhead. In the case of prolonged tunnel trips (the Chunnel, for instance) this rule can be amended to the first sight of the light at the end of the tunnel. Otherwise the singing of the song should be terminated upon the third time the driver threatens to stop and let you out inside the tunnel itself.
Enjoy this song and let it truly join the ranks of other such esteemed "travel songs" as 99 bottles of beer on the wall and Down by the Bay.