Canada’s energy capital, Calgary, rolled out a growth customer for natural gas produced by its corporate citizens: the city’s bus fleet.

Mayor Naheed Nenshi opened a cavernous, 477,000-square-foot garage billed as the largest indoor compressed natural gas (CNG) fueling complex in North America on Tuesday.

More than 470 buses, about half the current fleet in the city of 1.2 million, can park in the C$174 million ($130 million) structure near a natural gas pipeline.

After successful extended road tests of prototypes, civic plans call for eventually acquiring 400 or more CNG buses. Calgary buys transit vehicles at a brisk pace of 40-50 a year, depending on service demand and economic conditions.

“When fully operational, the facility will save taxpayers more than C$4 million ($3 million) per year on fuel costs,” the city’s transit department predicted. CNG replacements for diesel buses are also forecast to cut maintenance bills and greenhouse gas emissions.

“Investments in transit are among the best investments any city can make — they are investments in the environment, reducing congestion and improving mobility,” Nenshi said.