His idea started when he heard two religious workers playing music for free in New York City's underground transportation system.

VOA: special.2009.07.31

On Monday,two suicide bombings on Moscow's underground train system killed thirty-nine people.

VOA: special.2010.04.03

"These difficult to reach populations frequently go underground and remain not visible to the medical delivery system,"

VOA: standard.2009.11.15

looked at things like where should they locate waste water treatment facilities because of the impacts of climate change, what risks are likely to occur to their subway system because it's underground and already requires enormous pumping of water during certain large rainfall events."

VOA: standard.2010.06.14