The Houston Independent School District’s Transportation department has been ranked 13th among the top 50 green fleets in North America by the 100 Best Fleets in the Americas organization.

The winners of the 2015 Green Fleet Awards were announced during the National Green Fleet Conference in Columbus, Ohio, on Sept. 24.The most recent designation marks the fifth year in a row that HISD transportation has made the list.

Each year, the winners are chosen based on a comprehensive set of criteria centered on the challenges and requirements of maintaining a government fleet, including fleet composition, fuel and emissions, education and supporting programs. HISD is the only school district in Texas to make this year’s list, jumping up from last year from 17 to 13. The City of Houston also ranked on the list at 41.

“It is an incredible honor for our department to receive this award and be the top green school bus fleet in the nation,” HISD Transportation General Manager Nathan Graf said. “This speaks volumes about the hard work and commitment of all of our transportation employees.”

HISD operates and maintains more than 950 school buses that transport 34,000 students daily and travel more than 18 million miles annually. HISD Transportation uses about 2.1 million gallons of biodiesel, 600,000 gallons of gasoline and 400,000 gallons of propane each year. In addition, the district operates 91 propane buses and 20 light fleet vehicles that emit close to 0 emissions, with 30 more propane buses on order.

In an effort to maintain a green fleet, HISD has converted all of its school buses and diesel light-fleet vehicles to biodiesel derived from renewable sources such as soybeans, which is expected to reduce harmful emissions by up to 5 percent and extend the life of engine parts.

The 2015 Green Fleet Awards also will be announced in American City & Council magazine.