Merchandise Mart : Enviornment Friendly

I'm Very curious about how does this work???

Read the text below,
It's on the stickers pasted on the Merchandise Mart revolving doors..

Welcome to world's largest LEED-EB Silver Certified Building where every revolution reduces pollution..
FACT: If our 25,000 daily visitors used the revolving doors the pollution equivalent of 50 car trips from New York City to Los Angeles could be eliminated every year..