North American railroads are no strangers to rebuilding older locomotives to help lower cost. Unlike many parts of the world, the adhesion-limited operating environment often means that our locomotives are heavier and moderately powered. At one point in history, First Class Railroads have converged onto the ideal mainline locomotive, a six-axle unit having about 4,400 hp, and weighing at about 400,000 lbs.

NS 4005 sitting in South yard in Roanoke, VA.jpg
By Nstrainman1006 - Taking a photo. Previously published: YYYY-MM-DD, CC BY-SA 4.0, Link

In the 1990s, amid the market dominated by General Motors, the microprocessor-controlled Dash 9 Series was the revolution General Electric needed that kick-started their rise to the top. Within the series, there was the C40-9W, a limited-power edition of the mainstream C44-9W, specifically conceived for the Norfolk Southern. Starting in late 2013, these units were converted to the C44, and then two years later, some started further upgrades to, eventually, become the AC44C6M.

Compared to DC traction, locomotives with AC motors are vastly superior. They require less maintenance, and have better traction control, all thanks to the nature of the AC motors' design. Republic Locomotives has a fairly informative page on their advantages. As you can see in the video, at low speed and high tractive effort, the DC locomotive had a bit of a motor runaway. The AC44C6M is capable of producing 200 kips of starting, and 180 kips of continuous tractive effort, up from 142 and 106 kips as DC units.


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