The World Health Organisation has done extensive research on the impact of noise on sleep and their findings is that 32dB maximum sound (Lamax) inside a bedroom disturbs sleep with detrimental impact on health and well being and 35 dB (Lamax) wakes people up. The document can be read here (relevant data on page XIII of the executive summary).
At the consultation meeting on Wednesday 26 May 2011, a few people mentioned that they couldn't sleep in their basement or ground floor with the current noise from the tube in Kennington. There will be more trains (the Northern line will have more trains in general as part of their upgrade). And they will be going faster (as they will be going in a straight line and not around the loop as at present).
