When HS2 is fully operational, trains will thunder by at 200mph less than every two minutes. It will take the 400-metre-long trains around 4.3 seconds to pass any given spot but the noise could last up to 25 seconds in total.
The potential for disturbance is obviously huge.
HS2 Ltd says the pass-by noise from the train at 25 metres away will be 95db where no mitigation is in place or 76db where three metre noise barriers are employed.
It says the relatively few people living extremely close to the line can expect noise levels of more than 65 decibels in their homes, qualifying them for free sound insulation (of course, this won’t help people in their garden or if their windows are open).
Many more residents living slightly further from the line, including on the fringes of Aylesbury, can expect noise levels in their homes between 40-65dbs when the train passes.
HS2 Ltd admits 50db in the day and 40db at night can potentially cause ‘annoyance’ and ‘sleep disturbance’, while above 50db in the day and 65db at night ‘may be perceived as a change in quality of life for occupants of dwellings or a perceived change in the acoustic character of an area’.
To put this in perspective: A whisper is about 20db, a quiet library 40db, a conversation 50db, background music 60db, a vacuum cleaner 70db, a jackhammer 95db and a jet taking off 25 metres away 150db (which would cause your ears to rupture).
A change in noise levels of 5db is clearly noticeable, and a change of 10db sounds twice as loud as what came before.
HS2 is at pains to put out that its figures are all worst-case and how much of a disturbance the train causes will depend very much on the level of noise in the background – for instance from nearby traffic – and the topography of the area.
Noise is certainly very subjective.
During roadshow events people were able to listen to a recording of what HS2 Ltd projected the train would sound like.
The recording was widely ridiculed by HS2 opponents who claimed the birds singing in the background sounded louder than the passing train.
Campaigners are also sceptical over how HS2 Ltd compiled its noise data – claiming it has under estimated the impact.
The government agency says its trains and track will be designed to be as quiet as possible, using technology from East Asia.
Cuttings, sound bunds and noise fence barriers will further reduce noise, while tunnel portals, such as the ones in Wendover, will be ‘designed to avoid any significant airborne noise effects caused by the trains entering the tunnel’.
Of course, prior to those trains being operational, the line needs to be built.
During construction phase from 2019-2026, HS2 Ltd says it will keep noise down by using quiet equipment, control working hours and put up screenings.
It says monitoring data will be taken regularly and fed back to local councils.
Severely effected householders will be offered free noise insulation and even temporary rehousing – they will be identified at a later date. In its reports it is confident that, save for a few number of homes in Wendover, its mitigation measures will ‘reduce noise inside all dwellings from the construction activities such that is does not reach a level where it would significantly affect residents’.