NS SD70ACe

The SD70ACe is the successor to the SD70MAC with design changes to comply with emission standards. The engine fires with 15% lower internal pressure to improve emissions and features fewer internal components in the inverter.^[​8] SD70ACe is equipped with EMD's 16-710-G3C-T2 prime mover, rated at 4,300 horsepower (3,200 kW); later Tier 3 models are rated at 4,500 horsepower (3,400 kW).^[​9] They are rated at 157,000 lbf (700 kN) continuous tractive effort (191,000 lbf (850 kN) starting). Braking effort is rated at 106,000 lbf (470 kN).^[​9]

In 2012, EMD also built four models known as the SD70ACe-P6. These units, unlike previous SD70ACe's, have one inverter per axle on the trucks, rather than EMD's traditional one inverter per truck design.^{[citation needed]}

In 2014, BNSF Railway took delivery of 20 SD70ACe-P4 units, numbered 8500-8519. This model was designed with a B1-1B wheel arrangement to compete with GE's ES44C4 model, which has an A1A-A1A wheel arrangement. Two of EMD's demonstrator SD70ACe-P4's went to Tacoma Rail in late 2014 for a 5-year lease.

On January 1, 2015, the United States Environmental Protection Agency's Tier 4 locomotive emission regulations went into effect. EMD could not successfully modify the SD70ACe's 2-stroke 710 series prime mover to be Tier 4-compliant; thus, the Tier 3 SD70ACe was succeeded by the SD70ACe-T4 in late 2015. However, US production of the Tier 3-compliant SD70ACe continues with Tier 4 'credit units' (new Tier 3-compliant units EMD is entitled to build based on previously-earned emissions credits). Union Pacific and Norfolk Southern are currently the only US roads to own Tier 4 credit unit SD70ACe's. Additionally, EMD has continued building Tier 3 SD70ACe's for Ferromex (4100-4118), Ferrosur (4119-4133), and Kansas City Southern de Mexico (4200-4224) at Bombardier's locomotive plant in Ciudad Sahagún, Mexico. These locomotives are restricted to Mexico-only operation and cannot cross the US border (just as Canadian National's newest Tier 3 GE ES44AC's are restricted to Canadian use only).

In March 2016, EMD replaced the standard cast HTCR-4 trucks on NS SD70ACe 1000 with the new fabricated HTCR-6 trucks for testing. UP and BNSF plan to test the new HTCR-6 trucks on some of their SD70ACe units also.

Union Pacific Railroad received 273 additional SD70ACe units in 2014 and 2016. These are referred to as SD70AH (T4C) , H for Heavy, because they are ballasted to 428,000 lbs instead of the standard "ACe's" 420,000 lbs.