"white noise does not work on trains....try the device mentioned above in airplanes..record the noise of the train going past, loop it using a sample editor, burn it to cd and play it back at the same volume of the train when it goes past"

This is not 'white noise'. And this trick won't work anyway.

'Sound cancelling' techniques are not white noise.

"white noise which is very similar in frequency , played back thru speakers will cancel the sound to a significant degree"

No it won't- it will MASK the noise, NOT CANCEL it.

The 'white noise' trick works by raising the minimum ambient noise level, so that external noise is swamped in the 'floor' level.

'Sound cancelling' works by taking the original waveform and playing it back 180 degrees out of phase - there will be a minimum delay caused by the recording electronics, but the effect is minimal, and the cancellation works to an acceptable degree.