The sight impressed MP Charles Chong, who was visiting the Indian capital to find out how other cities juggle economic growth with protecting the environment.

'I thought, if India can do it, why can't we?' said Mr Chong, who chairs the Government Parliamentary Committee for National Development and the Environment.

The problem here, he found, is the cost of setting up a network of CNG refuelling stations.

Ten refuelling stations would cost around $40 million.

Singapore has only one, on Jurong Island, supporting more than 300 buses and taxis that have switched to CNG. Three more are due to open this year.

Hence the dilemma: save money or save the environment?

As countries across the globe relook their economic policies against the backdrop of climate change and shrinking natural resources, Singapore is no exception.

Last month, it set up an inter-ministerial committee on sustainable development that will find ways to keep the economy growing in an environmentally-sound way.

The move could result in pro-environment changes cutting across sectors such as housing, transport and trade and industry.

Mr Chong and other pro-environment MPs and environmentalists argue that the costs of green technology and infrastructure will translate to long-term gains in clean energy and air.

Insight explores the 'sustainable development' debate and the hard choices ahead for Singapore.

GOING GREEN - AND STAYING THAT WAY, INSIGHT