The Phoenix Public Transit Department has ordered 120 new buses to serve the city's routes.
It is first order for new 40-foot buses since 2013.
The buses use compressed natural gas and have a fuel range of at least 400 miles, meaning most of the new buses won't require daily refueling.
The new buses replace existing liquefied natural gas buses that average 12 years and 500,000 miles of service.
City officials say some of the existing buses are as old as 18 years with nearly 1 million miles.
The new buses are equipped with an enhanced air conditioning system that includes two units that work in tandem to cool both the front and back of the bus simultaneously.
The new buses replace about 25 percent of the city's fleet.