The number of residents in the city could put such a strain on its infrastructure by 2030 that the demand for power exceeds the supply, housing becomes scarce and rush hour lasts all day because of an overwhelmed transit network. Mayor Michael Bloomberg and a panel of experts warned Tuesday that the city of 8.2 million people must start planning and building now for the expected population growth of another million over the next 25 years. "We now have the freedom to take on the obstacles looming in the city's future and to begin clearing them away before they become rooted in place," Bloomberg said. A team of city planners, academics, scientists and environmentalists have spent the past year studying the city's infrastructure and assessing its viability for years to come. Some of them were assembled Tuesday to discuss their findings and begin mapping out possible solutions.