To date, Union Pacific is one of only two Class 1 railroads to order any SD70ACe-T4s. CSX also ordered 10 units in 2019, but returned them to Progress Rail in 2023. The SD70ACe-T4 is the EPA Tier-4 compliant engine built by EMD. So far, it has not proven nearly as popular as the ET44AC, the GE counterpart. UP 3059 is as example of an SD70ACe-T4, the first four-stroke diesel-electric locomotive that EMD has offered.
Even though the unit is less popular than the ET44AC, neither model has enjoyed wide ranging success. The maintenance cost (and complexity) of the Tier-4 units is a turnoff for railroads, and many are simply rebuilding old units at this point to save on money.
