it with the headlamps from the 389). Initially offered with a set-back front axle; a set-forward front axle was also introduced in 2015. In 2014, to commemorate 75 years of production, Peterbilt released a 75th Anniversary Edition of the Model 579, which was painted with a two-tone exterior and a matching interior. The Class 7 Model 220 underwent a redesign (the Class 6 210 was dropped), again mating a DAF LF cab (which underwent a redesign in 2013) to a Peterbilt-sourced cab and drivetrain. In 2015, the company introduced its first medium-duty trucks fueled by compressed natural gas (CNG), offering it as an option for the 337 and 348. The Model 388 was redesignated, becoming the shorter-length (123-inch) version of the 389. In 2016, the Model 520 was introduced, replacing the Model 320 after 29 years of production. While nearly visually identical to its predecessor (adding larger windshield wipers and optional LED headlamps), the refuse-collection functionality of the 520 was upgraded, allowing drivers to drive the vehicle sitting or standing from either side of the cab. In 2018, Peterbilt began testing on its first electric vehicle prototypes, building 12 579s and 3 520s with all-electric powertrains. 2020s In 2021, Peterbilt commenced production of three all-electric model lines, launching the Class 8 579EV tractor, Class 8 520EV low-cab COE, and the Class 7 220EV COE. The medium-duty model line underwent a complete redesign, as the 325, 330, 337, and 348 were discontinued. Adopting the larger cab of the 567 and 579, the Class 5-7 Model 535, 536, 537, and 548 also introduced the rebranding of several PACCAR drivetrain and suspension components. Models Current Medium-duty trucks (Class 5-7) Model 220 COE (Class 7, 2011-present) Model 535 (Class 5, 2021-present) Model 536 (Class 6, 2021-present) Model 537 (Class 7, 2021-present) Model 548 (Class 7, 2021-present) Heavy trucks (Class 8) Model 365/367 severe-service/vocational (2006-present) Model 389 extended-hood on-highway semitractor (2007-present) Model 520 low-cab COE, vocational/refuse (2016-present) Model 567 severe-service/vocational (2013-present) Model 579 aerodynamic-body on-highway semitractor (2012-present) Facilities From its 1939 founding to 1960, Peterbilt was based in Oakland, California, using the former Fageol facilities. In 1960, the company was required to relocate, moving to Newark, California. To supplement truck production, the company opened a facility in Madison, Tennessee (suburban Nashville) in 1969. Originally producing the 352/282 COE exclusively, the Madison facility added conventionals during the 1970s; the facility remained open through 2009. In 1975,