This week, I'll post about a locomotive that's quite close to our everyday life in North America.

We are no stranger to AC locomotives, and certain freight roads have been mass-adopting them since their introduction. For an adhesion limited tonnage railroad, one needs as much tractive effort as possible for trains to achieve their desired performance, be it steep grades and/or tonnage limits. Locomotives with AC traction motors satisfy exactly those requirements (here's a page on why). On top of the superior tractive effort than DC units, AC motors don't suffer stall burns and require less maintenance because they have fewer contacting moving parts. Of course, with the advantages comes the added cost of purchasing an AC locomotive, and some railroads aren't doing that because DC units suffice in their operating environments. This brings us to the locomotive I'm writing about today, the ES44C4.

Memphis National Train Day 2013.1 (8874348877).jpg
"Memphis National Train Day 2013.1 (8874348877)" by Matthew Nichols from New Albany, MS, United States - Memphis National Train Day 2013.1. Licensed under CC BY 2.0 via Wikimedia Commons.

The ES44C4 is a 6-axle AC locomotive from the Evolution Series produced by General Electric. However, unlike its cousin, the ES44AC, the ES44C4 has 2 fewer traction motors and has an axle arrangement of A1A-A1A (i.e. the middle axle of each truck is not powered). This gives the ES44C4 the ease of maintenance of an AC unit and the tractive effort of a DC unit. This also increases commonality between locomotives and helps the buyer to reduce the number of stock items. In addition, the unpowered axle on each truck of the ES44C4 can be raised to increase tractive effort when necessary (see the additional cylinders and linkages around the middle axle in the picture below).

BNSF 8013.jpg
"BNSF 8013" by CSX,LLC - Own work. Licensed under CC0 via Wikimedia Commons.

More details of the locomotive can be found on Wikipedia and here, from


M-NL said…
I totally do not understand the logic behind this: On a locomotive with an already ridiculously high axle load you increase it even further by lifting the middle axle. Using 6 smaller motors would have been better, because the tractive effort per axle is reduced, making wheel slip less likely.
Yes, you have a few less common parts, mainly different (cheaper!) motors and power electronics, but at the production numbers these machines are made in that's worth while.

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