THE M5O has been singled out as the worst noise polluter in Ireland, exposing nearby residents to an incessant din of traffic as loud as a twin-engine jet at takeoff.
The first "noise map" of Ireland estimates that traffic, especially on the M5O, causes the biggest racket. More than 23,000 Dublin residents live in the highest band of noise as a result of traffic. Dublin airport and the rail lines around the capital barely register a squeak.
The map, was drawn by Ireland's Environmental Protection Agency as part of the European Noise Directive that requires all countries to chart "unwanted or harmful outdoor sound" created by human activity.
Dublin was the only city to be mapped because it is large enough to meet the threshold, which requires measurement of urban areas with a population exceeding 250,000.
A sound level greater than 75 decibels (db) was recorded from the M5O. Researchers say that 70db is the equivalent of a passenger car travelling at 60 km/h and that 81db is akin to a twin-engine jet at take-off.
The map is a computer simulation based on data taken over one year regarding traffic volumes, frequency of public transport, population densities, the height of buildings, quality of road surface and other information supplied by councils and transport companies. No noise sensors were used to compile the map, but councils are now installing them to verify the data.
Key junctions such as the Red Cow roundabout and relatively small roads in Malahide, Donnybrook and along the Liffey quays are in the loudest noise category.
Tom Stafford, a senior scientific officer at the agency, said: "Because the map is based on annual data, and because there would probably be little activity at the airport or on rail at night this means almost all the noise is from major roads."
The population's exposure to noise is measured in Ldens, a logarithm based on decibels which gives a level based on combined day, evening and night readings. Night-time noise attracts a higher "annoyance score" than sounds occurring at day or evening time.
Most of Dublin's population of 1.2m people live in areas that have a sound level below the "noisy" 70 Ldens score. More than 141,000 people, however, live in areas that are exposed to more than 70 Ldens and 23,600 of them are in areas that experience the highest noise category recorded - greater than 75 Ldens.
Anthony Staines, an epidemiologist at Dublin City University said excessive noise was bad for human health. "It leads to hypertension, high blood pressure and affects childrens' learning ability," he said. "Sleep disturbance can also lead to daytime sleepiness resulting in accidents. Testing for noise pollution should form a much larger part of environmental impact statements, particularly when it comes to roads and airports."
Derek Keating, an independent councillor with South Dublin county council, said residents' complaints about the M50's noise pollution had been ignored. "Locals objected to the widening of the road but it went through anyway. Since heavy goods vehicles were removed from the city centre, it has gotten even worse," he said.
Margaret Errity, a psychiatric nurse who lives beside the M5O in the Woodfarm estate in Palmerstown, said she can no longer sleep with her windows open. "My house is the width of two lanes of traffic in distance from the motorway and the noise is constant. At night when it's less busy, the cars just speed up," she said.
After submitting the noise map to the European Commission, the local authorities must now formulate action plans, in consultation with the agency, to reduce the number of people affected by high noise levels.
The low noise levels from air and rail travel is likely to prompt councils to promote these modes of public transport over the use of cars.
Brian McManus, the head of Dublin city council's traffic, noise and air quality division, said the detail on the map would also enable the councils to plan better traffic management.
Ciaran Cuffe, a Green TD, hopes the government will reintroduce a noise pollution bill this year. "I want to see a one stop shop where people can go to complain about noise," he said.
Mark Tighe and Colin Coyle