Railway bonus for sounds without meaning?

At same A-weighted energy-equivalent level, railway noise frequently is preferred to road traffic noise. This effect often is called railway bonus. Among possible reasons for the railway bonus, differences in spectrum, time structure, and meaning of sound are discussed. In order to largely "neutralize" the meaning of sound, a procedure was proposed as follows: the sound, e.g. railway noise, is analyzed by Fourier-Time-Transform (FTT) and - after spectral broadening - re-synthesized by inverse FTT. The procedure has the advantage that the loudness-time functions of original and neutralized sound are identical, but the meaning of the sound is removed. In psychoacoustic experiments, for original sounds of railway versus road traffic noise, a railway bonus could be ascertained. If for the same sounds, when deprived from their meaning, also a railway bonus would show up, then the meaning of sound would contribute to the railway bonus much less than differences in spectrum and/or time structure. If, on the other hand, the meaning of sound would be a dominant factor for the railway bonus, with neutralized sounds no railway bonus should show up. Results of corresponding psychoacoustic experiments are reported and discussed in view of the psychophysical method used.