Freight and passenger rail rely almost exclusively on diesel power. The latest diesel innovations contribute to cleaner air and reaching climate goals.

According to the Association of American Railroads, in a typical year, US freight railroads move around 1.7 billion tons across nearly 140,000-miles of track. Since the 1930’s Freight trains have relied almost exclusively on diesel power due to its combination of power, performance, fuel efficiency, reliability, and durability.

According to the latest available data from the U.S. Bureau of Transportation Statistics (BTS), at the end of 2018 just over 26,000 freight locomotives were in operation in the US, and 431 passenger rail AMTRAK locomotives. Throughout the US from California to New York, state transit agencies operate regional rail services that are also powered predominantly with diesel engines. With the exception of a few passenger rail lines that are electrified (Amtrak’s Northeast corridor and Harrisburg, PA line), the remainder of passenger rail and all of freight rail in the country is diesel-powered. 

While the average car engine has about 200 horsepower, locomotive engines typically range from 2,000 to 4,500 horsepower. Train operators rely on diesel power across the full range of rail power applications. The smallest locomotive engines (up to 2,000 horsepower) are used in switch operations in freight yards to assemble and disassemble trains or are used in short hauls of small trains. The most powerful locomotive engines (up to 4,500 horsepower) are primarily used for long distance freight train operations by America’s five Class I railroads, short haul operators, and AMTRAK passenger rail locomotives.

Diesel engines have long held substantial economic and performance advantages over other power sources for locomotives. Recently, the potential for use of hydrogen and other fuel sources has been explored as additional options to reduce greenhouse gas emissions from this sector.

Advanced Rail Technology Delivers Clean Air and Climate Benefits

Diesel engine and locomotive manufacturers continue to improve engine performance while also lowering emissions. Since 2015, diesel engine technology in railroad locomotives has advanced dramatically following a similar technology pathway for heavy-duty diesel trucks and buses (low sulfur diesel fuel, enhanced combustion, particulate filters and selective catalytic reduction systems).

Today, the transformation to near-zero emissions in locomotive engines for every application is complete, with new engines manufactured beginning in 2015 now achieving the U.S. EPA Tier 4 emissions regulations for both particulate matter and oxides of nitrogen.

Railroad locomotive engines typically have long service lives of several decades, even as much as 50 years old, meaning that there is a large population of engines still in service that were designed before emissions standards were required. This means a much slower introduction of new, near zero emissions advanced diesel technology in the rail sector as compared to trucking. The benefits in emissions reductions and fuel savings of new technology diesel compared to older generations are considerable:

Replacing a single older switch locomotive with a new Tier 4 near-zero emissions diesel engine can generate the same emission reduction benefits as taking 8,000 cars off the road for a year.


Case Studies

Global locomotive manufacturer Siemens partnered with engine manufacturer, Cummins, to develop a near-zero emissions locomotive for AMTRAK’s aging fleet. Seventy-five new AMTRAK Charger locomotives entered service in 2021 powered with 4,000 HP Cummins QSK90 diesel engines that reduce emissions by 90% and are more fuel efficient that are reducing C02 emissions by 10% compared to previous generations of technology.

Rolls Royce Power Systems subsidiary MTU Solutions offers a hybrid PowerPak system that can be customized for any rail application to deliver a 25% reduction in CO2 emissions while also achieving near zero emissions with Tier 4 generation advanced diesel technology.

Machine learning can make machines more efficient. ProgressRail, a division of equipment manufacturer Caterpillar, integrated advanced electronic controls into the latest locomotive designs that couple Tier 4 near-zero emission reduction benefits with fuel savings performance. Longer unit trains often have several locomotive power units in front and rear of the train; known as a consist. The latest electronic innovations allow these engine to operate as efficiently as possible and eliminate idling to deliver superior fuel savings performance.

The Brightline highspeed passenger rail serving major cities in Florida is the nation’s only privately owned and operated intercity railroad. It also uses biodiesel to reduce the carbon footprint from its diesel locomotives by 20% which is the equivalent of removing 3 million cars from roads each year.