SPRINGFIELD, Ill. (WCIA) — The Sangamon Mass Transit District’s Board of Trustees approved on Monday a plan to integrate zero-emission buses into its fleet to replace the fleet’s aging diesel buses.

The SMTD currently operates 34 diesel-fueled buses and 22 compressed natural gas buses. The plan calls for the gradual replacement of diesel buses with hybrids and then the introduction of buses powered by hydrogen fuel cells.

“Since adding compressed natural gas buses to our fleet in the mid-90s, SMTD has been a leader in Illinois in running low-emissions buses,” said SMTD Managing Director Steve Schoeffel. “With 40 percent of our fleet CNG, we’re moving to change out our diesel fleet with diesel-electric hybrids, making our fleet fully low-emissions in the next ten years.”

For redundancy, the SMTD plans to always use at least two different types of fuel in the event a disaster or emergency eliminates one fuel source. The district said that unless a good alternative for CNG emerges, a portion of the fleet will remain fueled by GNG well into the future.

“We’re still planning studies to determine our next alternative fuel, but early research shows hydrogen fuel cell buses (HFCB) may be a better fit for our fleet, our operations, and our local climate,” Schoeffel said. “Any alternative fuel vehicle we decide to go with will be more expensive than diesel or CNG buses, and they will require fueling infrastructure. Right now, we’re leaning toward HFCBs, and we should be able to come to a more concrete decision in the next few years.”

The SMTD said that cost estimates for HFCBs exceed more than $1 million per vehicle, nearby double the current cost of a diesel vehicle. However, the district believes the reduced impact on the environment in local neighborhoods will be a benefit. The high cost is also why the district is moving in a “measured, deliberate manner.”

“We anticipate growing service needs and higher operational costs in the future, so we want to avoid saddling our successors with an unsustainable fleet replacement plan,” Schoeffel said. These decisions are quarter-century or longer decisions, and we will be as efficient as we possibly can be with the tax dollars we are responsible for.”

Much of the funding for the fleet’s transition is expected to come from federal grant funds.