The ES44C4 is the newest model in GE's Evolution series. Introduced in 2009, it is a variant of the ES44AC with an A1A-A1A wheel arrangement, reminiscent to EMD's E-units. It was designed to replace aging DC-traction units, such as the C44-9W, while still giving the benefits of six-axle AC traction. BNSF Railway was the first customer for this type, ordering an initial 25 units numbered 6600-6624.
A unique feature of these units is that there is a variable traction control system in their computer systems, the computer systems are the same as on CSX's heavy ES44AC's. One of the differences between an ES44AC and an ES44C4 are the air cylinders and linkages on the truck sideframes of the ES44C4; these are part of the traction control system. Every time a variable in grade, traction, or wheel slip occurs, the computer will adjust the pressure in these cylinders to maintain adhesion.
As of early 2016, BNSF Railway rosters nearly 1,000 ES44C4's (#6507-7199, 8000-8299, 8318-8399), and regional Florida East Coast Railway rosters 24 Champion scheme-painted C4's (#800-823).
in 2012, EMD introduced the SD70ACe-P4 model in direct response to the ES44C4. With a B1-1B wheel arrangement, the P4 is meant to compete with GE's A1A-A1A design in the same market. As of 2014, BNSF and Tacoma Rail are the only owners of SD70ACe-P4's.
2015: GE's locomotive plants are packed, with a backlog of two-three years. GE has Tier 4C units and production Tier 4 units under construction. The Tier 4 Credit units are the same as Tier 3 units under the hood, they have to be labeled as Tier 4C as part of the new regulations. GE earned credits by incorporating features into is EVO line that brought emissions under Tier 3 levels. GE has begun delivery of BNSF's first ET44C4 locomotives. These units are essentially Tier 4 ES44C4's. 3916-3917, 3920 and 3928-3934 have been delivered.
ES44C4 and ET44C4 orders for 2015 are:
BNSF: 161 ES44C4 Tier 4C; 161 ET44C4