Barcelona in Spain is a standout example of the benefits of TOD. In terms of population it is slightly bigger than Atlanta, USA (see graphic). However, dense, transit-oriented development has ensured that it occupies only 4% as much area as Atlanta that did not follow a TOD model. In the American city, residents drive long distances by car, resulting in 10 times higher carbon emissions.

Closer home in Ahmedabad, projections by Embarq—Centre for Sustainable Transport show that carbon emissions could increase 36-fold by 2041 if TOD is not implemented.

Is Delhi a fit candidate for TOD? Centre for Science and Environment (CSE) thinks so. Its analysis shows the city has a very sparsely populated core—only a sixth as dense as the administrative areas of New York or Madrid. Even the heritage area around the Louvre in Paris has twice the population density of Delhi's core. In fact, some Metro stations like Race Course Road and Jor Bagh on the crowded Yellow line are hardly used.

High-density development will reduce travel distances, so the air quality is bound to improve. Mumbai has fewer cars than Delhi "because its core is denser and perhaps people have to use public transport to commute," says Anumita Roychowdhury, head of CSE's Clean Air campaign.

At a time when a debate is raging on phasing out old vehicles and controlling air pollution with new vehicular and fuel technologies, Roychowdhury says, "TOD can complement technology-driven solutions". CSE sees Delhi's transport emissions rising to 526% of the 1990 level if no interventions are made to control vehicle population. TOD can help reduce vehicle use as its basic principle is that "you live close to the transit lines and there is walking and cycling infrastructure to get around in the area," she adds.

"Our simulations for Ahmedabad have shown a lot of improvement in air quality if development is along BRT and metro," says Amit Bhatt, strategy head, urban transport, Embarq India. He adds that TOD is not about mindless densification but diversity. "It will have mixed land use as well as mixed income groups living in the area which makes travelling efficient."

TOD has also worked in California which enacted Sustainable Communities and Climate Protection Act in 2008 to address increasing vehicle use. Between 1990 and 2008, per capita vehicle use in California increased by 3.5%. The state now has many priority sites for TOD.

"The proposed smart cities across India should ensure that they promote TOD to avoid future problems of congestion and air pollution," says Anup Bandivadekar, passenger vehicles programme director at International Council on Clean Transportation (ICCT). "Arlington County metro corridor near Washington DC is a great example of a TOD, but there are other examples from emerging economies across Latin America. It is important for the urban leaders to understand that TOD goes well beyond creating dense housing around transit options."