How can emissions be controlled?

With congestion increasing globally and emissions continuing to rise, many measures to reduce the potential increases are being considered. The move towards mega-cities with high densities, as in some cities in developing countries (e.g. 200-250 persons/ha in Chinese cities compared to 50 persons/ha in Western Europe) (World Bank, 2001) means that alternatives to individual four-wheel vehicles are essential. There are a number of routes being pursued to manage increases in traffic, due to three main factors: the economic costs of congestion, pollution control and limiting GHG emissions.