New Software Puts Rail Freight on Express Track to Net-Zero Emissions

Integrated System To Examine Full Network of Locomotives and Infrastructure for Deep Decarbonization Potential

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Nearly 200 years ago, workers drove spikes into the ground for the United States' first railroad tracks. Soon, rail lines crisscrossed the country, carrying people, goods, and industry to new frontiers.

Each year, more than 25,000 locomotives are used to transport 1.7 billion tons of cargo across the United States, which has the largest rail infrastructure network in the world. Rail freight is relatively efficient and clean, on average roughly 75% less carbon intensive than moving freight over roads.

At the same time, approximately 36 million metric tons of carbon dioxide is released each year in the movement of freight over rail. Shifting more freight from trucks to freight trains while reducing railway-related emissions presents significant promise as a strategy to meet broader needs for carbon emission reductions, also known as decarbonization.

Researchers at the Department of Energy's (DOE's) National Renewable Energy Laboratory (NREL) are collaborating with leading industry and research partners, including the University of Illinois Urbana-Champaign (UIUC), BNSF Railway, and Southwest Research Institute, on a new modeling framework that can be used to analyze and plan net-zero-emission and hybrid freight train systems. Soon, Advanced Locomotive Technology and Rail Infrastructure Optimization System (ALTRIOS) software will offer the first fully integrated package to optimize deployment of locomotive technologies, railway energy supply infrastructure, and train operating practices for cost-effective deep decarbonization. DOE's Advanced Research Projects Agency-Energy (ARPA-E) LOwering CO2: Models to Optimize Train Infrastructure, Vehicles, and Energy Storage (LOCOMOTIVES) initiative recently awarded $1.5 million in funding for the ALTRIOS project.

"Our need to decarbonize quickly promises a second great railroad revolution," ALTRIOS Principal Investigator and NREL Commercial Vehicle Lead Jason Lustbader said. "Trains have been around a long time, and they're still one of the most practical and energy-efficient ways to haul large quantities of heavy freight over long distances. But railways are complex systems, and we'll need breakthroughs and investment on multiple fronts to slash greenhouse gas emissions."

Railways' well-mapped set of fixed, high-density routes should make planning relatively straightforward. However, decarbonizing rail freight presents unique challenges in the form of requirements for propulsion power and interoperability between railway operators and locomotive types. Any strategies for decreasing emissions and energy use will also need to factor in the wide geographic distribution of fuel and energy supply infrastructure, high capital costs, and the long lifespans of the locomotive fleet. ALTRIOS will address these complexities with a flexible open-source modeling framework that will help to assess the feasibility of using various energy storage and electrification technologies such as batteries and fuels cells in heavy-haul freight railways.

NREL has long been a leader in innovation related to the energy efficiency of on-road vehicles, examining duty cycles and power requirements for specific vehicle vocational uses. The laboratory's engineers and scientists are now getting on board to apply this related truck research beyond the highway, seeking ways to cut emissions and energy use in other forms of transportation such as railways that can have very different operating characteristics.

Partner BNSF Railway is one of the nation's largest rail freight carriers. UIUC's Rail Transportation and Engineering Center (RailTEC) is the largest university railroad engineering research center and educational program in the country. Southwest Research Institute brings deep expertise in large-scale propulsion systems technologies and was a close collaborator with BNSF on testing a battery electric locomotive in California.

The team anticipates publicly releasing initial versions of the new suite of modeling tools in 2022.

A Challenging Switch in Technology Tracks

Many freight rail operators have already committed to pursuing significant greenhouse gas (GHG) emission reductions. Switching from today's standard diesel-electric locomotives to cleaner options such as battery electric, battery-diesel hybrid, and hydrogen fuel cell technologies can significantly decrease emissions. However, these systems will only work if they correctly match the right new, cost-effective propulsion, energy storage, and charging/fueling infrastructure technologies with the operational practices customized to support them.

A comprehensive, systematic study of all possible locomotive powertrain solutions and their effects on emissions from the freight railway system requires a transformation in modeling approaches. Currently, there is no single consolidated simulation tool that factors in the energy supply, locomotive, corridor, and network operations systems.

Most previous freight rail studies have compared locomotive technologies based on single-train or single-corridor simulations, neglecting to examine vital operational variables such as meeting and passing incidents, congestion bottlenecks, and detailed throttle/braking control decisions. Research also has typically not addressed the higher-level logistical issues of how to integrate alternative locomotive technology into existing railway operations.

"Other simulations have failed to factor in what happens when two trains meet, or they've oversimplified train performance and dynamics," ALTRIOS team member and NREL Manager of Advanced Vehicles and Charging Infrastructure Alex Schroeder said. "These might sound like subtleties, but they are magnified when you're weighing decisions at the scale of a rail system spanning the country. Tools like ALTRIOS are needed to help guide the billions of dollars in investments that rail operators and Congress are considering."

A Powerful Tool To Propel Change

ALTRIOS will provide the first open-source integrated software to evaluate and optimize efficient GHG emissions-reducing line-haul freight technology through simulations at the energy conversion and storage, locomotive, train, and corridor levels. The single unified simulation model will combine locomotive and energy storage technology models with robust train dispatching and corridor simulations and a high-level train planning tool.

Based on widely used open-source programming language, ALTRIOS will be made available free of charge online to policy- and decision-makers with the railroads, equipment suppliers, government agencies, and research institutions. Clear, easy-to-read outputs will help identify the most promising technologies for GHG reductions and help make related decisions on deployment of these technologies across train routes, types, and operations.

Other operational inputs used in ALTRIOS simulations will include acceleration patterns; distance traveled; location of fueling/charging infrastructure; number of tracks; locations of turnouts and crossovers; and sequences of train departure, meet, and pass events. Assessments will also consider external and regulatory factors such as railcar and train size/weight limitations, authorized speeds, headway separation, and grade and curve resistance.

"Although there are already smaller electric trains such as subways and light rail systems in operation, electrifying heavy-haul freight rail in North America is a different proposition. Industry estimates that locomotives will need batteries or fuels cells that are about 80 times larger than what you find in today's long-range electric cars. Solving the on-board energy storage challenge will be crucial to the successful use of renewable electricity or green hydrogen in these larger long-haul freight trains," Schroeder said.

A Flexible Solution Anticipating the Curves Ahead

Even though freight railroad fuel efficiency has doubled since 1980, and new locomotives are required to have criteria emissions 80% to 90% lower than pre-2000 levels, additional big breakthroughs are needed if the United States hopes to achieve net-zero-carbon-emitting cargo rail operations. These technological and operational improvements will also make it possible to shift more freight from long-haul trucks to trains with fewer emissions.

ALTRIOS will be invaluable for accelerating the development of climate-friendly freight rail innovation as well as billions of dollars in associated investments in rolling stock and infrastructure. This comprehensive, modular, open-source framework will guide private industry and government agencies in making the necessary investments in new technologies, locomotives, and energy supply infrastructure.

The tool needs to have the flexibility to assess new approaches that are still in early development stages. For example, partner BNSF recently began testing a battery electric locomotive that will reduce diesel fuel consumption on long rail segments and build on the company's fleet of cleaner, smarter machines such as electric cranes, loaders, and drayage trucks already in use at many of its railyards.

NREL will contribute its extensive experience in developing complex open-source simulation models, next-generation energy storage technologies, and real-world-validated transportation simulation models from the vehicle component to national systems scale. The laboratory's Eagle supercomputer, the largest HPC system in the world dedicated to advancing renewable energy and energy efficiency technologies, will also be used on the ALTRIOS project.

"Performance, efficiency, and emissions improvements need to be validated on a route-by-route basis. But even as technology and operations evolve, freight has to be delivered on time and within budget," Lustbader said. "Considering that freight locomotives are typically in service for up to 50 years and the current speed of technology, we need to make sure we're landing on solutions that will be flexible and also stand the test of time."

Learn more about NREL's transportation decarbonization research and the ARPA-E LOCOMOTIVES initiative. Statistics cited in this story were provided by ARPA-E, the Southwest Research Institute, the U.S. Department of Transportation, the U.S. Environmental Protection Agency, and the Association of American Railroads.