Diesel-electric locomotive, standard on American freight trains / Wikimedia Commons

Land-based long distance freight traffic in the US moves by rail and truck. Both modes rely on diesel fuel.

Freight electrification could lead to a significant drop in greenhouse gas emissions. This post concentrates on freight railway electrification, and especially the relatively new technology of battery-operated trains.

At the beginning of the 20th century, trains ran on steam engines. Two choices of more efficient locomotives emerged: diesel and overhead electric.

In the US, the railroad industry chose to convert to diesel because of lower up-front infrastructure costs. Elsewhere in the world, where governments owned the railroads, many systems electrified instead. Those that didn’t have already begun to transition to electric trains.

In the 1970s, the US government oversaw consolidation of seven bankrupt Northeastern railroads as Conrail. At that time, the US Department of Transportation and the Federal Railway Administration considered railway electrification.

They ended up rejecting it for that project but left the door open for it under other circumstances. They also rejected the idea of government mandates to electrify railroads. Subsequent examinations have also resulted in projects staying with diesel.

Diesel trains vs electric trains

In 2019, the transportation sector (including passenger cars, airplanes, and everything else) generated about 29% of all greenhouse gas emissions in the US. That’s the largest share of emissions of any sector, and most of it comes from burning fossil fuels.  Rail creates only about 2% of emissions from the transportation sector, but a shift from trucks to trains could conceivably reduce the sector’s overall emissions by 75%.

Diesel fuel accounts for more than 90% of the total energy consumption by the US freight rail system. And American railways transport more goods than any other freight rail system in the world. They currently carry 40% of all intercity freight in the US, and experts project its capacity to double by 2050.

If it still uses diesel at its current rate by then, it will account for half of the world’s diesel consumption for freight rail. Trains are more fuel efficient than trucks, but locomotives face less stringent pollution controls.

For example, locomotives must have catalytic converters to reduce nitrogen oxides and particulate matter, but unlike the ones on trucks, they have no requirement to reduce greenhouse gas emissions. Therefore, trains produce almost twice as much air pollution damage as trucks gallon for gallon.

With railway electrification, locomotives would emit nothing. Electric trains also offer other advantages:

• Where diesel trains transfer only about a third of the energy generated to the wheels, electric trains transfer about 95%.
• Electric trains are quieter than diesel trains.
• Electric trains also emit less air pollution than diesel trains: less particulate matter, volatile organic compounds, and oxides of nitrogen and sulfur.
• This reduced noise and pollution offers great health advantages in urban neighborhoods where trains operate.

Three technologies exist, or are in development, to replace diesel fuel: electrification of the rail system with overhead lines, hydrogen fuel cells, and batteries. As for the first two, zero emissions requires renewable energy with storage for electricity or green hydrogen.

Some principles of battery-operated trains

Norfolk Southern locomotive #999, a battery-powered 1350hp switcher / Wikimedia Commons 

Batteries for railway electrification deserve careful consideration.

For one thing, batteries have recently gotten both better and cheaper. Battery densities tripled between 2010 and 2020. At the same time, prices for battery packs fell 87%.

Some automobile manufacturers already offer lithium-ion battery packs for $100 per kilowatt-hour. By 2030, the industry-wide average is expected to reach $58 per kilowatt-hour.

Today’s diesel locomotives do not use diesel fuel to run the motor and drive the axles. Instead, the diesel fuel powers an electric generator that makes the train go. Technically, in other words, American trains mostly operate on diesel-electric locomotives. Replacing diesel fuel with batteries, therefore, does not require significant redesign of the locomotive.

Some train motors run on direct current and some on alternating current. Using batteries instead of diesel for direct current locomotives incurs negligible cost. Using them for alternating current locomotives requires a transformer and inverter. The batteries and, if needed, transformer and inverter add weight to the train.

But trains are now three or four times as fuel efficient as trucks. The rail system can easily absorb the extra weight. A single boxcar of battery cells will give trains all the range they need and still be more energy-efficient than a diesel-electric train.

Current regulations require 30-45-minute stops to change crews every 150-250 miles. A battery locomotive would therefore only need that much range. The stop would provide plenty of time either to recharge the battery car or swap it for a new one. Recent developments add another way to keep the battery charged: regenerative braking.

Battery-operated trains have arrived

Wabtec FLXdrive battery-operated locomotive / Railway Age

Battery-operated trains have been used for light duty, such as switching yards, for some time.

In September 2021, the freight train manufacturer Wabtec announced a successful test of the world’s first battery-electric locomotive, called FLXdrive. The battery consists of 18,000 lithium-ion battery cells and produces up to 4,400 horsepower to operate a train weighing 430,000 pounds.

It has a 2.4-megawatt-hour energy capacity and can recharge using both wayside charging and regenerative braking. That is, it captures the energy lost in the process of braking and uses it to recharge the battery.

FLXdrive operated between Barstow, California and Stockton, California. In three months of operation, it ran for a total of 13,000 miles.

An Australian mining company has already bought the first commercially available FLXdrive. But Wabtac and its collaborator Carneigie Mellon University have already started on a second-generation battery locomotive with a 7-megawatt-hour capacity. The mining company will likewise acquire the first available locomotive of the newer version.

Does it seem premature to announce that battery-operated trains have arrived on the basis of one successful test? I don’t think so. Tesla announced it’s Powerwall battery storage system in 2015. The following year it retired its first version in favor of a newer model with double the storage capacity and almost double the energy output. And now it has competition from other manufacturers.

Why wouldn’t battery-operated trains develop the same market penetration in the same amount of time?

Sources:

Don’t dismiss freight rail electrification / Jim Blaze, Railway Age. February 5, 2021
Economic, environmental and grid-resilience benefits of converting diesel trains to battery-electric / Natalie D. Popovich et al., Nature Energy. November 11, 2021
Electrification of U.S. railways: pie in the sky, or realistic goal? / Richard Nunno, Environmental and Energy Study Institute. May 20, 2018
The world’s first battery-electric freight train has the power of 100 tesla cars / Chris Young, Interesting Engineering. September 17, 2021