inconclusive, counsels "... against using the detailed results and conclusions [...] in the development of government policy." Air quality around airports is another major issue and a 2006 study found that levels of nitrogen dioxide exceeds EU guidelines at more than two-thirds of airports surveyed. Whilst aircraft contribute to the problem the study states that "…cars, buses and taxis ferrying passengers to and from these sites are dominant sources of pollution." Birmingham airport dismissed the findings, asserting that the results were skewed by M42 motorway traffic unrelated to the airport, whilst studies at Southampton Airport attribute 5.55 per cent of total pollutants to airport activities, the majority of the remainder being generated by non-airport related road traffic. The government recognises Heathrow as the only UK airport where national and European air quality limits are being exceeded. A provision of the original Civil Aviation Act allows designated airports to be required to provide facilities for consultation with affected parties, where local environmental concerns can be raised, and some 51 airports have been so designated. A 2000 consultation by the government re-iterated its policy that generally, local issues arising from airport operations are best addressed locally. To support this the Civil Aviation Act was extended in 2006 to give all airports the authority to mandate measures to address noise and air quality issues beyond their boundaries, and to impose financial penalties on aircraft which fail or are unable to adhere to such measures. The Civil Aviation Act 2006 also extends the provisions of section 78 of the original act, augmenting the powers of the Secretary of State to intervene directly in operations at designated airports; currently Heathrow, Gatwick and Stansted, "…for the purpose of avoiding, limiting or mitigating the effect of noise and vibration connected with aircraft landing or taking off." The largest airports also implement voluntary schemes to assist local communities in coping with the local effects of airport operations. Birmingham Airport, for example, has been operating a sound insulation scheme since 1978, in which 7,600 properties are eligible for sound proof glazing paid for by the airport. Schemes are also available to residents most affected by noise around Heathrow, designed to protect property prices ahead of any development of a third runway, assist with relocation costs for people who wish to move, and provide sound insulation for private and communal property currently affected by noise. In both cases local residents