although its air quality was generally good, parts of edinburgh suffered from high concentrations of nitrogen oxides (nox), mostly emitted from vehicle exhausts. minor traffic management changes were planned to reduce this by 5% in the worst-affected areas, but an overall 40% reduction was targeted, partly by introducing a low emission zone to restrict heavy goods vehicles, partly through improved vehicle standards, and the rest through edinburgh's 'integrated transport initiative', with journeys moving to public transport as a result of congestion charging.