Metrolink ordered 20 F125s in June 2013, becoming the first US operator to place an order for Tier 4 diesel locomotives. The 200km/h ac traction F125 is equipped with a 20-cylinder four-stroke Caterpillar C175-20 engine, generating an output of 3.5MW. The single-cab monocoque bodyshell was designed for EMD by Vossloh Rail Vehicles (now part of Stadler Rail) and features a crash energy management system to absorb energy in the event of a collision.

The locomotives, which are being assembled at EMD's plant in Muncie, Indiana, will also be equipped with VRV high-speed running gear and inverter-controlled head-end power.

EMD says the F125 is compliant with the US Passenger Rail Investment and Improvement Act's 305-005 Next Generation Locomotive specifications and offers an 85% reduction in emissions compared with older Tier 0 diesel locomotives. This is achieved through the use of a selective catalytic converter-only aftertreatment system and electronic fuel injection.