It is expected that more than 40 percent of the existing franchised buses will be retired by 2015, as an effort to promote wider use of environment-friendly buses, the local authority said Wednesday.

All pre-Euro and Euro I buses will be retired no later than 2012 and 2015 respectively, and Euro II buses by 2019, said Edward Yau, Secretary for the Environment of the Hong Kong Special Administrative Region government.

Yau told lawmakers if all pre-Euro, Euro I and Euro II commercial vehicles including franchised buses are retired, the economic benefit will be about 24.3 billion HK dollars (3.13 billion U.S. dollars).

He noted under a franchise requirement promoting wider use of environment friendly buses, bus companies must adopt the latest commercially available and proven environmental technologies when setting specifications for acquiring new buses.

All franchised bus companies in Hong Kong are required to operate their franchised bus services with buses under the age of 18.

The local government has also been working with the franchised bus companies to have them deploy more environment friendly buses to serve the busiest corridors.

Different options are being explored to reduce bus emissions, including accelerated replacement of old buses, bus route rationalization, establishing low emission zones, and assessing the feasibility of retrofitting selective catalytic reduction devices onto Euro II and III buses to reduce their NOx emissions.