Employment in the public transportation field represents about 13 percent of the nation’s clean/green jobs and the largest share of green-collar employment, according to Sizing the Clean Economy: A National and Regional Jobs Assessment, a report released July 13 by the Brookings Institution Metropolitan Policy Program.

Brookings worked with the Battelle Technology Partnership Practice to create the report, which it calls the first comprehensive study of the metropolitan geography of this economic sector, focused on the country’s 100 largest metropolitan areas.

“The clean economy sector is already an important source of industrial innovation, good-paying manufacturing jobs, and exports for a nation that needs them,” said Mark Muro, a senior fellow at the Metropolitan Policy Program and a co-author of the report. “Key segments show great promise for helping us use resources more efficiently, improving our national security, protecting our environment, and remaining competitive in rapidly-changing global markets.”

The report shows that the U.S. clean economy employs approximately 2.7 million people, more than the fossil-fuel industry and twice the size of the biosciences sector. It grew by 3.4 percent between 2003 and 2010—but newer clean energy and related segments of the clean economy grew by 8.3 percent during this period, nearly twice as fast as the rest of the economy. “Most clean economy jobs reside in mature segments that cover a wide swath of activities including manufacturing and the provision of public services such as wastewater and mass transit,” the report states. “A smaller portion of the clean economy encompasses newer segments that respond to energy-related challenges … the solar photovoltaic, wind, fuel cell, smart grid, biofuel, and battery industries.”

However, Muro said, other nations such as China and Germany have moved ahead of the U.S. in supporting clean economy development. He noted that China invested less than the U.S. in clean energy projects in 2004, but increased its funding to more than twice that of the U.S. in 2010.

Brookings also delineated the four main categories of clean economies in metropolitan areas: service-oriented, as in New York with its comprehensive public transportation system; manufacturing-oriented, more popular in the Midwest and South; public-sector, found disproportionately in state capitals; and multi-dimensional clean economies in such metropolitan areas as Atlanta, Los Angeles, and Portland, OR.

Accompanying the report are profiles describing the clean economy sector in all 50 states and in the nation’s 100 largest metro regions. A comprehensive mapping tool that allows users to see how the clean economy is distributed across the 50 states and in the 100 largest metropolitan areas, will also be available online.

The full text is available online.