Registering the Delhi Metro's contribution, the Germany-based validation organization TUVNORD conducted an audit on behalf of the UN Framework Convention on Climate Change (UNFCC) and gave its certificate.

"During the audit the organization found that the DMRC (Delhi Metro Rail Corporation) has stopped the emission of 90,004 tonnes of carbon dioxide from 2004-2007 by adoption of regenerative braking systems in the Delhi Metro trains," DMRC spokesman Anuj Dayal said.

Under the regenerative process whenever trains on metro network apply brakes, three phase-traction motors installed on these trains act as generators to produce electrical energy, which goes back into the overhead electricity (OHE) lines.

"The regenerated electrical energy that is supplied back to the OHE is used by other accelerating trains in the same service line, thus saving overall energy in the system as about 30 percent of the electricity requirement is reduced," Dayal added.

The DMRC saved 112,500 megawatt hours of power generation by restricting and reusing power on its trains through regenerative braking and in turn saving the emission of 90,004 tonnes of carbon dioxide. It is estimated that 39,000 tonnes of carbon dioxide were prevented in 2008 from being emitted and this figure will increase to over 100,000 tonnes per year once phase-II of the Metro project is complete.

DMRC can claim 400,000 carbon credits for a 10-year crediting period beginning December 2007 when the project was registered by the UNFCC.

"The money available from sale of carbon credits will be used to offset the additional investment and operation costs incurred due to the implementation of the project, to stimulate research and development activities by DMRC to develop technology to reduce emission of green house gases and to give extensive training to train operators for optimum regeneration," Dayal added.