These are the greenest places to work in Houston

HOUSTON (KTRK) -- Some of the highest-profile Houston employers are also the most environmentally conscious, according to a new ranking from city officials.

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The city released its 2016 Houston Green Office Challenge winners this week, and engineering firm Walter P Moore once again took home top honors. METRO came in second place, and urban design firm Asakura Robinson Company came in third place. The Houston Zoo claimed first place in the non-profit category, and NASA Johnson Space Center won for property management.

Challenge participants attended a variety of workshops aimed at helping corporations improve economic and environmental performance in the workplace. After two months, participants reported back on how they had worked to improve their energy and water efficiency, waste reduction and transportation.

A Walter P Moore representative said the challenge helped the company analyze water use, cleaning practices and waste disposal. METRO committed to offset 30 percent of its electricity use over a five-year period.

NASA specifically focused on employee transportation programs.

"The goal is to build a culture where sustainability becomes commonplace and accessible. The number of 'free-range' bikes grows each year, employees have vanpooled for years, and the fleet of electric vehicles continues to expand," NASA/Johnson Space Center's Program Specialist for Sustainability Stacy Shutts said of the agency's sustainability goals.

"The Green Office Challenge is a great example of how the public and private sectors are working together to make Houston the greener, more sustainable community we see today," Mayor Sylvester Turner said in a news release. "Congratulations to the 2016 winners for their outstanding performance and to all participants for helping Houston set an example for other cities to follow."