I never seen a train overtaken by another train in a parallel adjunct track lane. Usually there are trains bypassing opposite direction to each other from parallel track lanes. 

I think it would be easy to distinguish with confidence if the passing train sound comes initially from your back or from your front. 

Additionally you would be aided by the [Doppler-shift][1] effect of sound of the bypassing train that initially will increase in pitch and then lower in pitch as the two trains separate.   

  


  [1]: https://en.wikipedia.org/wiki/Doppler_effect