In an effort to reduce its carbon footprint and stay ahead of state zero-emission guidelines for transit agencies, the Orange County Transportation Authority will introduce a fleet of 10 hydrogen fuel cell electric buses and make upgrades to its Santa Ana bus base.

The new fleet will cost about $12 million and expands on a 2016 pilot program that brought in one hydrogen fuel cell bus. It will replace existing buses that run on compressed natural gas.

The cost is a mix of OCTA and grant funds through the California Air Resources Board and the South Coast Air Quality Management District.

The buses will run on popular routes such as 29, 47, 53, 55 and 64, which serve Anaheim, Garden Grove, Orange, Santa Ana and Westminster. They will be integrated into OCTA’s fleet of more than 520 buses in January 2019.

“With advances in the operation and reliability of hydrogen electric buses, OCTA wants to continue to enhance efforts to provide reliable public transportation while using the cleanest technology available,” said OCTA spokesman Eric Carpenter. “The clean-burning hydrogen fuel cell buses release absolutely no greenhouse gases into the environment.”

Houston-based Trillium CNG will begin construction of hydrogen fuel distributors — which will fill each bus in six to 10 minutes — at OCTA’s Santa Ana facility, which it built in 2007 and continues to maintain, later this year. The station will be able to fuel up to 50 buses.

The $4.7 million construction price tag will be funded through a grant from the Low Carbon Transportation Investments and Air Quality Improvement Program.

Unlike buses that run on fossil fuel, hydrogen fuel cell electric buses emit only water instead of air pollutants. Compressed natural gas is categorized as near-zero emissions.

“OCTA has a long history of implementing clean sustainable technology into our fleet. As we look toward the future, it’s important we continue expanding these efforts,” said Cliff Thorne, OCTA’s director of maintenance and motorist services.

Over the past two decades, the agency has retired diesel buses in favor of CNG-powered ones.

“While compressed natural gas remains a high priority for Trillium, diversification of customer needs, products and services within the transportation industry is driving our expansion,” said Bill Cashmareck, managing director for Trillium CNG. “Each alternative fueling source has its own set of benefits, and we want to meet the needs of our customers in as many ways as possible.”

The agency has no plans to expand the hydrogen fleet beyond the incoming buses.