Calgary Transit is launching two new buses fuelled by compressed natural gas.

Drivers took the buses on a test drive Monday. The buses will go into revenue service starting Tuesday, with two more joining the fleet in May. Calgary Transit officials will spend more than a year monitoring how the buses run given the city's climate.

"They're cleaner, they're quieter, they're more economical, and it makes sense for Calgary Transit to be in the lead in proving the worth of natural gas buses throughout the natural gas economy given where we sit," said Mayor Naheed Nenshi.

The buses cost about 30 per cent less to operate than traditional diesel buses and are much quieter.

Routes changed Monday

Some Calgary Transit commuters may have noticed changes to their regular routes on Monday morning.

The public transit provider adjusted service to 19 routes, including the Cranston/Bridlewood Route, which will now service the new South Health Campus hospital.

Calgary Transit says the changes are based on ridership statistics and feedback from staff and users. Service adjustments happen four times a year.

Watch a Calgary Transit employee give a tour of a new bus