In cases of very high pollution, cities such as Beijing or Delhi have introduced 'odd and even numberplate' traffic regulations. For example on the 8th December 2015 in Beijing. The schemes can have an impact on traffic and pollution in the short term in extreme situations - but at the cost of significant inconvienience. If they become longer term measures, then their impact reduces, as has happened in Athens (Greece) where they are adopting emissions aspects to improve the odd and even scheme. Outside Europe, in Tehran (Iran) found that their odd-even scheme was no longer effective, and are now implementing a low emission zone. While odd-even schemes can sometimes be useful in extreme pollution events, it is better to work in a more planned way to ensure that the pollution levels reduce so that they do not reach the high levels. In Europe we have long had measures such as vehicle emission standards ('Euro standards"), low sulphur petrol and diesel (which reduces emissions). These can be combined with long term local measures, such as low emission zones , congestion charging and traffic limited zones are more effective for traffic. For more information on other things that are done to improve air quality, see our page on what else is being done to reduce air pollution.