The Phoenix Public Transit Department plans to add up to eight new buses each week through July as part of an order for 120 buses that will replace about 25 percent of the fleet. 

The cost is $62 million or $520,000 per bus and is paid for by federal funds and from Maricopa County’s Proposition 400 funds.

It’s the first order for buses since late 2013.

The buses, built in California by the Gillig Corp., use compressed natural gas or CNG and have a fuel range of at least 400 miles.

The new buses will replace buses fueled by liquefied natural gas or LNG that average 12 years and 500,000 miles of service. Some are as old as 18 years with nearly 1 million miles.

Each Gillig bus is 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 Phoenix Public Transit Department is the largest member of the Valley Metro regional transit system.