The Phoenix Public Transit Department ordered 120 new Gillig Compressed Natural Gas (CNG) buses to serve the city’s local routes — the first order for new 40-foot buses since late 2013.

The CNG buses, built in Hayward, Calif. have a fuel range of at least 400 miles, which means most of the new buses would not require daily refueling. The new buses replace existing liquefied natural gas buses that average 12 years and 500,000 miles of service, some as old as 18 years with nearly one million miles.

Each Gillig bus is also 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.

Five to eight buses will arrive each week now through July, and as they do city staff will inspect each one to ensure all equipment is in working order, as well as install the farebox. Once a bus clears inspection, it is sent to one of Phoenix’s three bus yards and then put into service.

The Gillig order replaces about 25% of the city’s bus fleet.