The world's largest network transports 16 million passengers on 8,000 trains every day, spreading 300,000 litres (60,000 gallons) of human waste from "open-discharge" toilets, transportation expert Ganesan Raghuram told the gathering.

"We are probably the only railway system in the world that has open-discharge of faecal matter," said Raghuram of the Indian Institute of Ahmedabad in western Gujarat state.

"Apart from the bad smell, the problem is becoming a lot more significant because of the public costs."

Raghuram advocated an aircraft-style vacuum system to replace the old-fashioned toilets that contaminate soil and water -- particularly when monsoon rains wash the accumulated waste into rivers and lakes.

"There is so much to learn from how ships have done it, how aeroplanes have done it, how houseboats have done it. But Indian Railways are still not doing it," he said.

Rail tracks and fittings also wear out faster than they should due to corrosion from the faecal matter and urine, he added.

He called on public-interest lawyers to sue the railways for failing to improve its toilets.

Indian Railways, which nearly went bankrupt six years ago, posted a 4.4 billion-dollar surplus this year.

Raghuram estimated that it would cost approximately one billion dollars to fit coaches with vacuum toilets and storage tanks.

Other delegates also suggested low-water use tank storage systems, with the possibility of suction extraction at terminals.

Some 170 delegates from more than 40 countries met in New Delhi from Wednesday for the World Toilet Summit to discuss how to bring low-cost, environmentally-safe toilets to millions of people, mostly in developing countries.

About 2.6 billion people -- more than 40 percent of the globe's population -- do not have access to proper toilets.

The United Nations wants to halve that number by 2015 as part of its Millennium Development Goals.

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