EMD SD70MAC
by
Mike Gerenday
The SD70MAC was produced by EMD from 1993 to 2004 (with an exception) using a 16cyl 710 producing 4,000hp with later models producing 4,300hp. There are many variant of the SD70 aside from the MAC, but since the ARR only has the MAC variant we'll just discuss this one.
Built in response to GE's C44-9CW, the SD70MAC was built with safety cabs, HTCR trucks, and 3 phase AC traction motors. M designates wide or safety cab, AC for Alternating Current. The later models that produced 4,300hp had the SD45 style flared radiators. The HEP equipped SD70MAC was only ordered by the Alaska Railroad. The SD70MAC was replaced by the SD70ACE with over 1,100 locomotives produced.
Starting in 1997, the ARR leased a pair of EMD demonstrators to test the abilities of 6 axle power. At the time, the ARR still had most of it's original alignments on the south and north ends, which limited prior 6 axle power such as SD40-2 locomotives. There has been other 6 axle power on the ARR such as ALCO RSD-1, MRS-1 and EMD E9 locomotives, but were shorter or didn't have full powered trucks.
After successful tests the ARR decided on ordering 16 brand new SD70MAC locomotives. Rostered 4001-4016 these were placed in service in late 1999 and early 2000. The locomotive components were built in the EMD plant in London Ontario and assembled in the Junita shops in Altoona Pa. The original order did not have HE equipment so HEP equipped GP40-2 locomotives were used with the 4000s on the passenger trains. At this time power cars were still used on passenger trains as well.
In 2004 a second order of eight locomotives arrived and were put into service, these were HEP equipped SD70MACs rostered 4317-4324. Then in 2007 the last SD70MAC locomotives rostered 4325-4328 were put into service in time for the 2008 summer season. Traditionally the ARR numbered it's diesel locomotives to reflect both the horsepower and the number in the class. The ARR decided to continue the 4xxx roster and not create a new class for the 43xx locomotives. The 4325-4328 were the exception to the 2004 production end of the SD70MAC.
In the early 2000s the ARR experimented with the MAC's DPU capabilities with successful results. DPU means Distributed Power Units, this means locomotives can be place in strategic locations on long freight trains for both tractive effort, and to keep air pressure in the brake lines up to par. As trains get to a certain length the air pressure starts to drop, and in colder temperatures such as we have in Alaska, the air pressure really drops, so by adding locomotives in the middle this keeps air pressure up, and more cars could be added. DPU trains are common on Anchorage-Fairbanks freight trains.
The paint scheme on the SD70MAC locomotives are basically Alaska's version of BNSF Grinstein scheme used on their SD70MACs. Early in the 2000s, the ARR re-built and re-painted several GP locomotives in a version of the new scheme which has now become the standard scheme used on many locomotives. The ARR SD70MAC locomotives are the newest locomotives on property and have become the main staple of the fleet. As of 2020 all SD70MACs are in service, some have had major repairs and upgrades over the years. One engineer friend told me that our SD70MACs have the least amount of miles than the ones in the Lower 48 states, so it's safe to say these big girls will be around for years to come. To learn more about the SD70MAC click here.
Page created 1/2/21 and last updated 1/2/21