SCAX 905, the first F125 delivered to Metrolink, unveiled at Los Angeles Union Station.
The EMD F125 Spirit is a four-axle passenger diesel locomotive manufactured by EMD for the North American market. It is powered by a Caterpillar C175-20 V20 diesel engine rated at 4,700 hp (3,500 kW). The locomotive is capable of traveling at a maximum in-service speed of 125 mph (201 km/h) pulling consists of up to 10 cars. It is EMD's first new domestic passenger locomotive in 15 years, with the previous passenger locomotive being the EMD DE30AC and DM30AC built for the Long Island Rail Road.
Features of the F125 include EPA Tier 4 emissions compliance (with exhaust after-treatment), AC traction systems, extended-range blend and dynamic brakes with HEP regeneration capabilities, advanced crash energy management (CEM) technology, and a streamlined body design, designed by Vossloh Rail Vehicles of Spain. The locomotive is equipped with two Nathan AirChime K2 horns, with the primary horn mounted under the forward coupler, and the backup horn placed on top of the locomotive.
The Los Angeles commuter rail agency Metrolink is the launch customer for the EMD F125, with an order of 40 total. The cost of the base order of 10 units with an option of additional 10 was estimated at $150 million, with delivery commencing in 2016. The base order was signed on May 31, 2013 for 10 locomotives with an option for additional 10,  which has since been exercised. Additional orders were exercised as funding became available. They will replace the EMD F59PH and EMD F59PHI.
The first locomotive, SCAX 903, began testing in the first quarter of 2016. The bulk of the order was expected to be delivered by April 2017, but as of June 2017, 13 locomotives have been delivered. The first one delivered, SCAX 905, was unveiled on July 18, 2016 at Los Angeles Union Station during a special event, and had its first mainline run on June 10, 2017.
As of March 2018, major problems with the EMD locomotives have prevented their full acceptance by Metrolink and few locomotives are in full revenue service. Metrolink's problems with the F125's have served as caution for other agencies, resulting in no significant additional contracts for the EMD F125. By contrast, Siemen's competitive Tier 4 locomotive, the "Charger", continues to rack up major contracts such as Amtrak's acquisition in December 2018 of 75 Chargers for long distance train services.
- "C175-20 Prime Mover Specifications". Caterpillar Inc. n.d.
- "Locomotive Capacities and Specifications". EMD. Retrieved June 16, 2017.
- Bowen, Douglas John (December 20, 2012). "EMD gets Metrolink Tier 4 locomotive order". Railway Age. Retrieved May 27, 2016.
- "Metrolink orders EMD passenger locomotives". Railway Gazette International. June 1, 2013.
- Jeon, Yena (January 24, 2014). "F125 Tier-4 EMD Status Report". Metrolink. Retrieved May 27, 2016.
- Templeton, Dan (July 19, 2016). "Metrolink F125 locomotive unveiled in Los Angeles". International Railway Journal. Retrieved December 4, 2017.