For widespread freight rail electrification to work again on a large scale in the U.S., there is a need for a new generation of all-electric locomotives designed specifically for the U.S. freight market. At the present time, the all-electric locomotives being manufactured in the U.S. are designed for passenger service, most notably the Siemens ACS-64. However, an in- production electric locomotive could be adapted for short-haul U.S. freight service. The Bombardier IORE European freight or the Siemens ACS-64 U.S. passenger locomotives could be modified to U.S. freight standards, but pulling lighter and faster trains than an interstate line-haul U.S. freight train. It is also possible for an existing U.S. line-haul freight locomotive model, with its higher weight, tractive effort and six-axle chassis, to be converted to all-electric by replacing the diesel engine with a catenary pantograph and transformer system.
Electric freight locomotives in Western Europe tend to be less powerful than their U.S. counterparts, which leads to a common misconception that all-electric locomotive technology is not powerful enough for U.S. freight rail. However, heavy all-electric freight trains used in China, Russia, Australia and South Africa are more appropriate electrification examples for U.S. freight rail. In fact, the heaviest all-electric ore and coal trains in these countries are much heavier than U.S. line-haul freight trains.
The weight of a long-distance, U.S. line-haul freight train ranges between 10,000 and 20,000 short tons. The most powerful diesel-electric locomotives used in U.S. freight service are the 6,000 hp GE AC6000CW (840 kN starting tractive effort, 740 kN continuous) and EMD SD90MAC (890 kN starting tractive effort, 734 kN continuous). However, U.S. freight railroads have moved away from such high-horsepower locomotives as they have found it more efficient to use multiple locomotives, of less than 5,000 hp each, as distributed tractive power in the front, middle and/or rear of a train. An example of a more typical large Tier 4 U.S. line-haul diesel-electric locomotive currently being manufactured is the EMD SD70ACe-T4 (4,600 hp, 890 kN of starting and 780kN continuous tractive effort).
An electric locomotive can be designed to match or exceed the performance specifications required by U.S. line-haul freight trains. In fact, the world’s most powerful locomotives are all-electric. In China, a single HXD1 two-section, all-electric locomotive set (19,300 hp, 1,140 kN starting tractive effort) is the most powerful locomotive currently used in the world, pulling entire 20,000-ton coal trains. For the 535-mile Sishen–Saldanha Orex line, South African Railways uses a 50 kV catenary system for hauling 41,000 metric ton (46,000 short ton) ore trains. These trains are pulled by up to nine all-electric Mitsui Class 15E locomotives (each with 6000 hp, 580 kN starting tractive effort) in distributed configuration, not unlike that of a U.S. line-haul freight train.