CN ES44AC

The ES44AC (Evolution Series, 4400 HP, AC traction) replaced the AC4400CW model in the General Electric catalogue. These locomotives have been ordered by every Class I railroad in North America: Union Pacific Railroad (who refers to these locomotives as the C45ACCTE), BNSF Railway, CSX Transportation, Norfolk Southern Railway, Kansas City Southern Railway, Kansas City Southern de Mexico, Ferromex, Canadian Pacific Railway, and Canadian National Railway.

The Class II Iowa Interstate Railroad ordered 14 ES44ACs (IAIS 500-513) in 2008 to handle an expected traffic growth resulting from new ethanol plants coming on line. An additional 3 locomotives (IAIS 514-516) were delivered in 2016 and three more (IAIS 517-519) were delivered in late 2019. As a result of the delivery of the final six locomotives, the Iowa Interstate will retire its SD-38 fleet. The IAIS 513 is painted in a Rock Island, Route of the Rockets heritage paint scheme, and the IAIS 516 is painted in a Rock Island inspired scheme celebrating the 30th anniversary of the start-up of the railroad.

CSX began receiving an order of 200 ES44ACs (referred to by CSX as the ES44AH) in December 2007. The A is for A.C power The "H" in the class CW44AH and ES44AH units refers to the HTE ("high tractive effort") adhesion-management software with which those units are equipped. The reason CSXT has assigned specific classes to units equipped with that software is that the software allows the units to have increased tonnage ratings and is in reference to a combination of subsystems that produce high levels of tractive effort at low speeds. In order to be classified as an "AH" by CSX, a locomotive has to have not only an increased nominal weight (currently to 432,000 pounds [​216 short tons; 196 t]), but also (1) steerable trucks, (2) TM3 adhesion control software, (3) software that extends to 33,000 pounds-force (150 kN) from 30,000 pounds-force (130 kN) the maximum amount of tractive effort that each traction motor is permitted to produce, and (4) GE's Rail Cleaner, which directs high-pressure air onto the rails in front of the sand nozzles forward of axle number one.

In September 2008, Norfolk Southern purchased 24 ES44ACs numbered 8000-8023, and began receiving the first of these units in October 2008. Ordered to be used on long haul coal trains, they were the first new AC locomotives ever purchased by NS. An additional 65 units were ordered in 2011, numbered 8025-8090. 24 more units, numbered 8091-8115, were ordered at the beginning of 2012. 10 of these units: 8025, 8098-8105 & 8114 were painted in predecessor company "heritage" paint schemes for NS's 30th anniversary. All NS ES44ACs are built to CSX specifications, with the exception of the Hi-Ad trucks & headlight placement.

In March 2008 Cemex took delivery of one ES44AC, number 81, built to the specifications of CSXT units 700-839 as an add-on to that order.^{[citation needed]}

Canadian National's first order of ES44ACs was in January 2012, and as of 2018 they roster about 236 units, numbered in the 2800-2999 and 3800-3835 series. With the introduction of the United States Environmental Protection Agency's Tier 4 locomotive emission regulations, CN's newest Tier 3 GE ES44AC's are restricted to Canadian use only.

Citirail/CREX acquired 100 ES44ACs for lease service. They are painted silver with blue & yellow nose striping and blue numbers. Most, if not all of these units,^{[weasel words]} were leased to BNSF Railway. In June 2021 Canadian National purchased all of Citirail’s ES44ACs.^{[citation needed]}

In 2013, General Electric built one ES44AC, GECX 3000, as a test bed for their NextFuel natural gas power kit.^{[citation needed]} The engine runs on liquefied natural gas from a fuel tender. The unit has since been converted to a battery-electric locomotive to be tested on BNSF trains in California.