Bio Edit

The EMD (Electro Motive Division) SD70MAC is a type of six-axle, AC-traction, 4,000hp (later units rated at 4,300hp) diesel locomotive built from 1993 to 2004 (while production briefly resumed from 2005 to 2007 for orders from the Alaska Railroad).

BN #9417: one of the many SD70MAC units delivered to the railroad from 1993-1995 prior to the BNSF merger in 1996.

Over 1,100 units were built total. Over 100 were originally built specially for the Burlington Northern (BN); the original customer (while orders continued on into the BNSF merger with an additional 600+ units), while only 15 were delivered for Conrail in 1998, and were assembled at the railroad's Juniata Locomotive Shops in Altoona, PA. Later customers such as CSX, ONR, the Alaska Railroad (ARR), and TFM (subsidiary of KCS; Kansas City Southern) eventually purchased units prior to the introduction of the SD70ACe.

The SD70ACe serves as the SD70MAC's initial successor: having more advanced microprocessor controls, a higher horsepower rating, and being EPA Tier 2-compliant, for the SD70MAC doesn't quite follow all regulations issued by the agency and is Tier 1 certified.

It is essentially the AC-traction version or variant of the SD70M, though the SD70MAC is regarded as being the very first ever commercially successful AC-traction diesel locomotive built for the North American market, as well as being the first commercially successful AC-traction model built by EMD. Although not the first AC-traction model built, the F69PHAC built in 1989 served as a stepping stone for the model and its subsequent precessor: the SD60MAC, for the F69PHAC was indeed the very first ever AC-traction locomotive built for the North American market.

Its rival, the GE AC4400CW, outsold the model in greater quantities, however, and was more popular amongst railroads like CSX, CP, and UP.

Many are still currently in service, with the exception of several stored, wrecked, and subsequent retired units.

History Edit

During the early-1990's, EMD teamed-up with German engineering company Siemens to experiment with having an average, modern, North American type of traditional DC-traction freight diesel locomotive become capable of providing AC-traction: something that was never originally achieved. AC traction-motors, while simpler and more reliable than DC-traction motors, require expensive inverters and rectifiers to generate a variable-frequency AC signal, raising the locomotive's purchase cost substantially. However, they further provided a high-horsepower rating and lower fuel consumption for railroads which had an ever-increasing demand for reducing operation costs along with fuel consumption by using a lesser amount of units to haul most of their trains. The solution to all these problems was resolved with the experimental SD60MAC, which proved to be a success after several demonstrations with the Burlington Northern's Powder River coal trains between Wyoming and Montana. Because of the success of the SD60MAC, the development for the SD70MAC; the first commercially-successful AC-traction production locomotive model ever built by EMD, became well underway. Although the SD60MAC was successful, the BN; however, disliked the cab design due to being uncomfortable with rail employees who tested the units. Such complaints consisted of: heavy vibrations, noise pollution from the prime mover, and an unusual amount of cab visibility due to the cab design originating from an earlier SD60M, yet with a slightly different window placement which deemed to be too "foreign"; meaning that the design looked more Canadian and such design was originally disliked by employees who drove some of BN's earlier SD60M units ordered and received several years earlier.
Conrail SD70MAC's

A pair of Conrail (CR) SD70MAC's hauling a coal drag through the eastern Appalachian mountains.

The SD70MAC was first introduced in early 1993, and began production later-on during the same year after numerous tests and improvements were made. The first orders of 75 units were received from the BN in mid-1993 to late-1995; with orders placed the previous year in 1992 as a result of the SD60MAC's initial success and the railroad's effort to contribute over $675 million to order 350 SD70MAC units total. As a result, BN began to slowly replace their fleets of aging SD40-2 units (aside from their subsequent GE U30C and C30-7 3,000hp DC-traction units) assigned to their Powder River coal trains in favor of their new, modern, high-tech AC-traction SD70MAC units; which were proven to replace 5 to 7 SD40-2 units on an average coal train on a 3 to 4 basis; meaning that only 3 to 4 would be necessary (two front, two rear or three front, one rear) during said heavy-haul application. Furthermore, with the SD70MAC units being equipped with DPU (Distributed Power Unit) and CTE (Controlled Tractive Effort) capabilities (which were originally introduced with the SD60MAC), anything was possible.

Towards the end of the SD70MAC's debut, a new rival from GE appeared: the AC4400CW, which completely dominated over the SD70MAC in production sales. Although more successful in popularity, the AC4400CW didn't prove to be popular with either owner or customer whom previously ordered or presently owned SD70MAC's except for CSX and BNSF; yet CSX didn't acquire SD70MAC's or SD70AC's until after the 1999 Conrail split, while BNSF didn't place orders for their fleet of 150 AC4400CW's until 2001. Both models are often regarded as the locomotives responsible for starting the so-called, short-lived, "power race" between the two builders which occurred from around 1995-2002.

Today, the SD70MAC can still commonly be seen assigned to coal drag service on BNSF, as well as being a common hauler on KCS (Kansas City Southern). All Conrail SD70MAC units can still be seen on the CSX system, yet no longer retain their once-exclusive livery which was very similar to their distinct SD80MAC livery. The Alaska Railroad's fleets of SD70MAC units can still be seen in general revenue service on both of their freight and passenger trains (being the only US Class 2 railroad to actually have both revenue freight and passenger service as well as being the only regional company within the state). Said units are equipped with HEP generators and are Tier 1-compliant under the US EPA's strict emissions policies.

Most later production SD70MAC units were also built with distinct flared radiators (reminscent of the SD45) to comply with the US EPA's once-strict "Tier 2" policy. Said units are often classified as the SD70MAC "Phase 2", while the one's ordered by CSX are often designated as the "SD70AC" and are built to similar specifications like their ES44AH units.


Although the SD70MAC may seem like a completely different locomotive model, it's essentially just the AC-traction version of an SD70M (unlike the GE AC4400CW, which is actually meant to be a completely different locomotive model) with additional exterior and interior components which primarily help reveal the SD70MAC's distinct AC-traction drivers, invertors, and microprocessor computer control features (the radiator cabinet
CSX 4577 SD70MAC

Although CSX differentiates between each of their AC-traction models from their subsequent DC-traction counter-parts using distinct "lightning bolts", units like #4577 (an SD70MAC) however, never received such distinction.

cover with vents and louvers behind the cab being the main noticeable difference, aside from a large gap with more distinct vents and louvers being present at the rear hood of the actual locomotive).

The "AC" suffix serves as an additional designation or suffix for the SD70MAC being an AC-traction version of the SD70M, while the "M" officially stands for "modified", to which the SD70M was originally modified from the original SD70 model (having a "wide-cab"), while the SD70MAC is generally meant to be the AC-traction version of the DC-traction SD70M.


Production Dates 1991-1992 1993-2004 (2005-2007)*
Total Built 4 1109*
Length 74' 0" 74' 0"
Wheel Arrangement C-C C-C
Engine 16-710G3A 16-710G3C-ES
Horsepower 3,800 4,000 to 4,300
Alternator TA17/CA7A TA17/CA7A
Traction Motors 1TB2630 1TB2630
Weight x 1,000 lbs. 390 415-436

Note*: SD70MAC replaced by Tier 2-compliant SD70ACe in 2005. SD70MAC continues to be available for export sale (as of 2005). Total includes ARR 4325-4328, Tier 1-compliant SD70MAC's built in 2007.


One SD60MAC unit was actually rebuilt into an SD59MX demonstrator in 2010-2011. Like with their other fleets of AC-traction diesel locomotives, CSX adds or paints distinct "lightning bolts" on the sides of the cab just below the numbers on their SD70MAC units (including their SD70AC's). Conrail's SD70MAC fleet was originally meant to be compatable with their SD80MAC fleet as well, yet their SD70MAC's commonly served as helper or DPU units on trains led by SD80MAC units. Said diesels of the latter were commonly operated in pairs (two front, two rear, and sometimes two mid train, and vice-versa).

The SD70MAC was the last type of locomotive ever purchased by the Burlington Northern (BN) before merging with the Santa Fe (ATSF) in 1995-1996, which also wore a short-lived exclusive paintscheme (known as "Grinstein Green" after ex-BN CEO Gerald Grinstein; also known simply as "Green and Cream") which was also applied to their executive fleet of now-preserved F Units and coaches inspired from one of their predecessors (being the Great Northern).

Norfolk Southern (NS) originally intended on ordering a small fleet of SD70MAC units to suppliment their existing SD80MAC's inherited from the Conrail split, but received "Phase 3" SD70M's instead.

BNSF #9647; the "Vomit Bonnet", was painted in an exclusive livery to commemorate the success of the BNSF merger, but once demonstrated an experimental scheme. The unit is now currently in "Heritage 3" (H3) paint.

Only a handful of SD70MAC units have actually been painted into BNSF's H3 ("Heritage 3") scheme. BNSF's later SD70MAC units had different headlight and handbrake placements as opposed to their earlier pre-merger/post-merger BN SD70MAC units.

ARR #4001 was actually applied with a unique dedication known as the "Spirit of Alaska", similar to CSX's "Spirit Of..." units.

CSX has since auctioned or sold-off the vast majority of their SD70MAC/SD70AC fleet to the Paducah And Louisville shortline, for the parent company (owner of the shortline) has since been in the process of acquiring more ES44AH/ES44AC units to replace them.

Two ex-CSX SD70MAC units now owned by the Paducah And Louisville (PAL) shortline were recently repainted into exclusive liveries dedicating local sports teams: the Louisville Cardinals (PAL #2013) and Kentucky Wildcats (PAL #2012). Both units share similar liveries with existing GP38-3 (ex-GP40-2) rebuilds (nos. 1998 and 3801), while #2013 and #3801 share one with long-retired GP10 #1798 (a GP9 rebuild).


Sources Edit

Conrail SD80MAC Pt2 of 509:51

Conrail SD80MAC Pt2 of 5

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