Do you mean the pedestrian underpasses or the underground trains? Because the noise level in an underground train station is significantly less than at street level, it just seems louder because it is intermittent.
The SPL on the London Underground reaches maximum levels of >105dB (previous measurements on the Northern Line hit ~108dB, IIRC). Average noise levels on some parts of the deep underground lines (Victoria, Northern, etc.) can be well in excess of 80dB.
Comments
Do you mean the pedestrian underpasses or the underground trains? Because the noise level in an underground train station is significantly less than at street level, it just seems louder because it is intermittent.
The SPL on the London Underground reaches maximum levels of >105dB (previous measurements on the Northern Line hit ~108dB, IIRC). Average noise levels on some parts of the deep underground lines (Victoria, Northern, etc.) can be well in excess of 80dB.