How to improve railroad fuel efficiency

[ Below are excerpts from this 70 page report. It is hard to find documents on reducing oil consumption through energy efficiency, most papers concentrate on greenhouse gas emissions, which usually lowers energy efficiency, or how to grow roads, rail tracks, and ports to handle the infinite growth in the future.  Alice Friedemann

Update: RR have continued to improve their efficiency since this paper was written, from 403 ton-miles to 476 miles in 2015 (see “When trucks stop running” for details.)]

Stodolsky. 2002. Railroad and Locomotive Technology Roadmap. Center for Transportation Research Argonne National Laboratory,  United States Department of Energy.

The approximately 4 billion gallons of diesel fuel that are used by locomotives each year is about 10% of the total diesel fuel used in transportation and 2.3% of all the fuel used in transportation in the United States (Davis 1997). Large freight carriers consume most of this fuel. U.S. railroads spend over $2 billion per year, or approximately 7% of their total operating expenses, on diesel fuel (AAR 2002). Because fuel costs represent a significant portion of the total operating costs of a railroad, fuel efficiency has always been an important factor in the design of locomotives and in the operations of a railroad. In terms of energy efficiency, these are dollars well spent. An important measure of rail energy efficiency is revenue ton-miles per gallon of fuel consumed. A revenue ton-mile is one ton of a customer’s goods moved one mile. Simply stated, it measures the amount of real work that freight railroads do for their customers for every gallon of fuel used. (Passenger railroads use passenger-miles per gallon for a similar measure.)

America’s railroads have dramatically increased the number of ton-miles delivered per gallon — from 235 in 1980, to 332 in 1990, and then to 403 in 2001, which is an increase of over 71% (AAR 2002). This achievement was due to the combined effect of many technological advances and improvements in dispatching and operations, as well as to shifts in the mix of commodities transported and to longer shipment distances by dense commodities, like coal.

The U.S. Environmental Protection Agency has established strict emission standards to be implemented in stages (Tiers 0, 1, and 2) between 2000 and 2005. Locomotives currently emit over one million tons of NOx each year, which is about 5% of total NOx emitted by all sources (Orehowsky 2001).

Some of the technologies that could be employed to meet the emission standards may negatively affect fuel economy — by as much as 10–15% when emissions are reduced to Tier 2 levels.

Lowering fuel economy by that magnitude would have a serious impact on the cost to the consumer of goods shipped by rail, on the competitiveness of the railroad industry, and on this country’s dependence on foreign oil.

The ability of locomotive manufacturers to conduct research into fuel efficiency and emissions reduction is limited by the small number of locomotives manufactured annually. Each year for the last five years, the two North American locomotive manufacturers — General Electric Transportation Systems and the Electro-Motive Division of General Motors — have together sold about 800 locomotives in the United States. With such a small number of units over which research costs can be spread, outside help is needed to investigate all possible ways to reduce fuel usage and emissions.

An estimated 43% of the gain came from the increased share of ton-miles represented by coal and other dense commodities (Vyas 2001).

The railroads, their suppliers, and the federal government have embarked on a cooperative effort to further improve railroad fuel efficiency — by 25% between now and 2010 and by 50% by 2020, on an equivalent gallon per revenue ton-mile basis. They also expect to meet emission standards and achieve these goals in a cost-effective, safe manner. Achieving these goals will save 700 million gallons of fuel per year by 2010 and 1.3 billion gallons of fuel per year by 2020, at current traffic levels.

This effort aims to bring the collaborative approaches of other joint industry-government efforts, such as FreedomCAR and the 21st Century Truck partnership, to the problem of increasing rail fuel efficiency.

DOE plans to bring similar efforts to bear on improving locomotives.

Although it may be possible for the railroad industry to benefit from developments in the trucking industry (which is faced with a faster schedule for emissions reductions on a g/bhp-h basis), railroads have unique characteristics that pose different challenges than those facing the trucking industry: 1. Locomotive engines have larger bores and lower speeds, which means that fuelsystem modifications developed for trucks cannot be directly transferred to locomotives; 2. Engine cooling is more difficult; consequently, engine air temperatures (which affect NOx formation) are much higher than ambient; and 3. Long expected life (40 years) requires substantial built-in durability and the need to retrofit the many locomotives in service.

On the basis of the research objective of improving total railroad average fuel efficiency by 50% by 2020, the government’s portion of funding for locomotive and railroad R&D to achieve this is estimated to be about $20 million annually for about 14 years, to bring funding on a level consistent with that of heavy trucks.3 Assuming that the goals are met and railroad average fuel efficiency increases by 50% in 2020 (savings begin in 2005) and remains constant thereafter, a total of 600 million barrels of oil will be saved between 2005 and 2030. On the basis of this assumption, about $0.46 of government funding is expended per barrel of oil saved. With an estimated average industry cost-share of 25%, total R&D funding is about $0.58 per barrel saved.4 These estimates exclude effects from a shift of freight from trucks to rail, which would further increase energy efficiency and improve cost-effectiveness. Additional global benefits will accrue from the sales of (1) advanced locomotives and train systems overseas and (2) engines for marine applications.

TABLE S.1. Potential Research Topics

Train Systems

  • Operations Optimization
  • Consist Management
  • Aerodynamics
  • Wheel/Rail Friction
  • Rolling Resistance

Locomotive Systems

  • Idle Reduction
  • Energy Recovery
  • Motors and Drives

Locomotive Engines

  • High-Efficiency Turbo
  • Sensors and Controls
  • Fuel Injection/Combustion
  • NOx Adsorber
  • PM Trap

Advanced Powerplants and Fuels

  • HCCI
  • Alternative Fuels
  • Fuel Cells

The DOE R&D budget in fiscal year 2002 to improve heavy truck fuel efficiency is $88 million. Assuming this funding continues until 2010, and considering past funding starting in 1996 on heavy trucks, a total of $1.1 billion will have been spent by the government. According to DOE, cumulative energy savings from heavy truck advanced technology will be 2,384 million barrels by 2030. (Source: facts_quality_metrics_). Applying this cost-benefit to railroads, total R&D funding needed would be $280 million over about 14 years, or an average of about $20 million each year.

Costs exclude capital equipment, infrastructure costs, and production costs needed to implement the technology.


U.S. railroads spend over $2 billion per year, or approximately 7% of their total operating expenses, on diesel fuel. New emission standards — to be implemented in stages between 2000 and 2005 — may reduce the fuel efficiency of new locomotives by as much as 10–15%. With the potential to substantially increase operating costs and further erode already tight net operating income, meeting those standards could become a major obstacle to the economic health of the industry.

Today, over 3.5 trillion ton-miles of freight are transported each year by five modes: rail, truck, water, pipeline, and air.

Unfortunately, most of the techniques for reducing NO x also decrease the fuel efficiency of the engine and raise PM emissions. This decrease in fuel efficiency would have a serious negative effect on the financial stability of the railroads and, thus, provides an additional urgency to finding ways to improve fuel efficiency. As is shown in Figure 6, the decreases in fuel efficiency to achieve the Tier 1 limits are expected to be between 5 and 15%


Although it may be possible for the railroad industry to benefit from developments in the trucking industry, which is faced with a faster schedule for emissions reductions, railroads have unique characteristics that pose different challenges than those of the trucking industry.

  • Trains have much less freedom in choice of speed because their schedules must be coordinated with those of many other trains on the same track. In addition, locomotives must be able to pass through long tunnels, limiting the size of mechanisms that can be attached to the exterior and producing special challenges with respect to thermal management.
  • On-road trucks have large exposed radiators in the front, and with speeds usually maintained above 50 mph, ample air (ram air) is available for both engine and aftercooler cooling. In contrast, locomotives usually run in consists (i.e., groups) of two or more, often run in “reverse” or in the middle of the train, and spend most of their time at speeds below 45 mph. The radiators are mounted in the roof and cooling fans are required to remove engine heat. Air-to-air after-cooling is difficult; consequently, engine air temperatures (which affect NOx formation) are much higher than ambient.
  • Trains have less flexibility in operations because they cannot change their routes to go around a problem, and they may need to sit on a siding while another train passes.
  • Locomotive engines, which have up to 6,000 horsepower, are, of course, much larger than truck engines. Their larger bores and lower speeds mean that fuel-system modifications developed for trucks cannot be directly transferred to locomotives, although many of the approaches (e.g., higher pressures, multiple injections, shaped injections) could be used in modified form. Also, locomotives have considerably less power per ton carried than do trucks.
  • Truck engines are coupled directly to a mechanical transmission and are required to operate over the entire engine speed and load map, whereas locomotives employ a diesel-electric system and only eight specific power settings (notches). Notches correspond to eight set engine speeds.
  • Locomotive engines are expected to last for at least 40 years, which places greater emphasis on durability. This low turnover rate also limits the penetration rate of new technologies; however, locomotives undergo many overhauls, providing opportunities for modifications throughout their lives.
  • Diesel fuel for locomotives can contain 10 times more sulfur than diesel fuel for trucks contains. Sulfur contributes to formation of engine-out particulate matter, corrosive exhaust gases, and rapid poisoning of some aftertreatment devices.
  • Whereas trucks are severely limited by weight and size, it is relatively easy to add another car, such as a fuel tender, to a train when more space is required for additional equipment. However, adding a car that does not carry freight can impact the productivity of the train.8

The diesel engine is the most efficient transportation power plant available today.

Thermal efficiency of locomotive diesel engines is 40% or higher, which results from high power density (via high turbocharger boost), high turbocharger efficiencies, direct fuel injection with electronic timing control, high compression ratio, and low thermal and mechanical losses. Many locomotive engines achieve the equivalent of one million miles before overhaul (36,000 megawatt-hours).

A focused research and development program could enable the locomotive diesel engine to achieve thermal efficiencies of 50-55%, resulting in a reduction in specific fuel consumption of about 20%.

Meeting the technical targets for high efficiency and simultaneously reduced emissions will require advances in four areas: in-cylinder combustion and emission control, after-treatment, thermal (exhaust gas) management, and sensors and controls.

Trains rely on high friction under locomotives to keep wheels from slipping and sliding when power is applied. Past studies have indicated that energy savings could be as high as 24% when friction at the wheel/rail interface is properly managed. Friction is also required under braking conditions to control train speed down hills or to bring a train to a safe stop. Much lower friction levels are desirable under normal train operations and can significantly reduce the energy required to pull a train. Therefore, the key is to apply the lubricant just where it is needed and to make sure that it does not cover the track where high friction is needed for traction or braking.


A significant fraction of the energy consumed in rail transport is due to wheel/rail friction. The magnitude of the wheel/rail frictional energy losses relative to other losses (bearings, aerodynamic, and grade) depends on the condition of the track (dry or lubricated), whether the track is curved or tangent, truck design, wheel rail profile conformance, truck wear resulting in poor steering, and train speed. Typically, for curved track, a 33% reduction in the rolling resistance can produce a 13% reduction in total resistance, while for tangent track, a similar reduction produces a 3% reduction in total train resistance.

Technical Barriers. Reliability of devices for applying lubricants to the rail or wheel flange is the major barrier to wider use. The devices must operate in very harsh environments. Locomotive-mounted lubricators may cause excess lubricant to migrate to carriage underbodies and truck sides, which increases the potential for fires and produces a difficult environment for maintenance operations. Lubricant from either wayside lubricators or locomotive-mounted lubricators may migrate to the top of the rail, where it causes poor traction. Concerns about TOR lubrication include buildup of lubricant on the rail, reliability of applicator devices, and compatibility of TOR with flange lubrication.


There appears to be little room to improve the aerodynamic design of locomotives. However, considerable aerodynamic-drag losses are found for certain car configurations, especially those that include empty coal cars and intermodal cars. One company has found that aerodynamic drag accounts for about 15% of the round-trip fuel consumption for a coal train, and that fuel consumption is approximately the same for an empty train as it is for a full one. In an experiment with simple fairings or foils (not a full cover) to direct the air flow over the empty cars, about a 25% reduction in aerodynamic drag was achieved, which resulted in a 5% fuel savings for the round trip. For intermodal cars (two containers stacked on a flat car), about 30% of the energy loss is due to aerodynamic drag.

Potential for Fuel Savings. Coal transport consumes approximately 1.5 billion gallons of fuel annually; a 5% savings due to reduction of aerodynamic drag would be 75 million gallons, or 2% of total Class I railroad fuel consumption. The primary challenge is to develop a system for covering empty coal cars that does not interfere with loading and unloading and that does not require much time to install. Other challenges are limited maintenance requirements and high reliability and durability.


The fuel cell is generally considered to have the greatest potential for replacing the internal combustion engine on vehicles. When one considers that present day locomotives are electrically driven (via direct overhead wire, third rail, or diesel-generator set electrification), the fuel cell can potentially replace both diesel-electric and electric locomotives if the technology can progress to be physically feasible and economically viable. With the potential for high efficiency and very low emissions, this technology has been monitored for many decades with great interest; however, the technical and economic challenges have inhibited serious commercialization plans.

Locomotives require significant horsepower for transport.

Fuel-cell technologists have made significant progress in demonstrating devices with higher power density. While recent advances in power density may enable consideration for locomotive applications, much work remains to demonstrate adequate operational life and to develop highly efficient methods to reform (or process) hydrocarbon fuels to generate sufficient quantities of hydrogen for the locomotive application.

Fuel cell research needs to be conducted with a focus on components that, when integrated together as a total system, will demonstrate an operational utility equal to or better than the electric and diesel-electric locomotives presently in operation or contemplated for the future.

Information in the public domain generally indicates that current programs for automobile and stationary power applications will not meet locomotive application requirements; therefore, dedicated research for the locomotive propulsion system is required.

Some of the unique application requirements for the locomotive include (but are not limited to):

  • physical size
  • vibration and shock
  • operational temperature range
  • voltage magnitude and electrical-current output capability
  • sufficient fuel storage to enable an operational range equivalent to present locomotive operations with No. 2 diesel fuel
  • reformer technologies for fuels having higher energy demands

Potential for Fuel Savings . The thermal efficiencies of fuel/cell reformer combinations and diesel engines are roughly equivalent, so a direct replacement of one for the other would have little effect on fuel efficiency, until an inexpensive, low-impact H2 source is developed. The main driving force for fuel cells, of course, is emissions reductions.

Technical Barriers. Important technical barriers remain for application of fuel cells to locomotives.  Efficient reformation of hydrocarbon fuels is a major barrier, which greatly counteracts and negates the efficiency gains from the fuel-cell stack.

Most fuel-cell R&D does not address the more stringent locomotive operational environment. The locomotive application does not generate interest among researchers because the annual production volume for locomotives is extremely small compared with much higher-volume applications (e.g., automotive). Whereas automotive volume may enable lower fuel-cell cost, those devices will not be applicable to a locomotive without dedicated research to meet locomotive requirements.

Sulfur levels in many fuels are too high for most present or proposed fuel-cell systems.

Requirements for the fuel-cell auxiliary and support systems remain a packaging challenge.

Suggested R&D. The following research activities would be necessary to develop fuel cell technology to a point at which it would be suitable for locomotives. • Intensify research for storing larger quantities of hydrogen safely and reliably. • Initiate a broad research program for reforming hydrocarbon fuels specifically for locomotive application. • Continue research toward higher kilowatt output per unit volume and weight for the most promising fuel-cell technologies (PEMFC, SOFC, PAFC). • Continue research for providing either (1) fuel-cell devices that are more tolerant of impurities in the air and hydrogen supply systems or (2) air supply and hydrocarbon fuel reformers capable of delivering purity levels required by the respective fuel-cell technologies.


Potential for Fuel Savings. The gas turbine has no potential for fuel savings compared with a diesel engine, but it could be used to reduce emissions.

Technical Barriers. Gas turbines are continuous-combustion heat engines and therefore have the ability to burn a wide variety of gaseous and liquid fuels. Impurities, such as vanadium and sulfur, that affect the high-temperature parts, are problematic, but gas turbine combustors can be designed to burn most environmentally friendly fuels, such as natural gas, hydrogen, synthetic fuels, and alcohols. In the past, high cost and low-duty-cycle efficiency have been the biggest technical barriers to the application of gas turbines on U.S. railroads.

At low-duty factors, high fuel consumption at idle and low load make the turbine uneconomical. A typical railroad duty cycle puts a 5,000-horsepower gas turbine at a 25% fuel consumption disadvantage compared with today’s locomotive diesel engine.

The cyclic load profile of the typical locomotive is a challenge to gas turbines. Locomotives experience several full load swings per hour. The typical aircraft gas turbine sees one cycle per flight, and power plant turbines see nearly constant speed operation. Transience is also a problem for gas turbines in terms of fuel efficiency.

First cost is another significant barrier. The typical cost of a 5,000-horsepower gas turbine is roughly the same as the entire diesel locomotive, which is three to four times higher than a comparable diesel engine. If gas turbine locomotives are to be widely utilized, the higher first cost of the turbine must be offset by its environmental value and operating costs.


There are two main methods for supplying power to electric locomotives: an overhead wire system (catenary) or a third electric rail. High-voltage AC currently provides most overhead power supply. Higher voltages, with less current, limit heat losses in the overhead transmission of electricity; however, there is a trade-off because of potential hazards and the need for costly on-board equipment to use the higher voltages. Power levels of about 25 kilovolts are used in new catenary systems and represent a compromise of efficiency and cost.

Locomotive electrification is well established in the industry. It is useful where rapid acceleration is important, such as some commuter rail systems, but it is not currently economical for long-haul freight service.


The use of alternative fuels in locomotives could help reach national goals related to fuel diversity, use of domestic energy resources, energy efficiency, and lowering of exhaust emissions. However, most alternative fuels, with the exception of biodiesel and oxygenated diesel (oxydiesel), cannot be used directly without substantial modifications to engine and locomotive systems, as well as to the refueling infrastructure.

Alternative fuels are most readily used in the trucking industry by fleets having central refueling and maintenance facilities

The truck and bus industries have conducted fleet studies to compare the performance of natural gas, ethanol, methanol, and biodiesel with that of diesel fuel. These fleet studies have shown that alternative-fueled vehicles generally have higher operating and maintenance costs than conventional diesel-powered vehicles. The operating costs can vary significantly because the fuel price is strongly dependent on the location of the fleet operation. Maintenance costs are generally higher for alternative-fueled vehicles since their technologies are less mature.

Natural gas in CNG or LNG form shows promise because of lower NO x and PM emissions and favorable environmental image. Use of CNG or LNG typically adds 15-25% to vehicle cost as compared with diesel-fueled vehicles because of the higher cost of the engine and fuel storage and delivery systems. In addition, on a BTU basis, LNG costs about 60% more than diesel fuel. Field tests of a CNG-powered locomotive by the Burlington Northern Railroad in the mid-1980s showed that CNG is impractical for wide-scale railroad use because of its relatively low energy density (Fritz 2000). However, LNG has a considerably higher energy density, and locomotive engines have been successfully converted to operate well on LNG.

While LNG can produce a 60% reduction in NO x and some decrease in PM compared with a conventional diesel engine, the amount of unburned HC and CO from a LNG engine can be much higher (Fritz 2000).

Technical Barriers. The primary barriers for alternative fuel use are not technical — they are cost, market acceptance, reliability, and deployment. Because of the additional cost of most alternative fuel technologies, an incentive (such as lower alternative-fuel cost or a perceived threat of a fuel shortage) will be required to create a market for their use. The primary barriers for the use of natural gas pertain more to fuel storage and refueling facilities. If extra fuel tanks are required, then space availability on the locomotive can be a barrier.

The primary barriers for Fischer-Tropsch diesel are economic. Feedstock would be most economically available in remote locations where large quantities of natural gas are available, but capital costs for production facility construction would be high in these locations because of a lack of general infrastructure. Fischer-Tropsch diesel also could be produced from solid fuels (such as coal) through a gasification step, but that would require additional capital investment in the fuels-processing plant. The abundance of coal resources in the United States could make this option more attractive if supplies of natural gas become tight. Direct firing of micronized coal/water slurries has been investigated, but that process requires very deep and potentially expensive processing of the coal to remove ash and other contaminants, as well as extensive modifications to the fuel-handling and injection equipment on the engine. Reliability of the engine and fuel equipment is another barrier.

The primary barrier for biodiesel, oxydiesel, and water/diesel emulsions is high production costs. Additionally, untreated biodiesel has issues related to oxidation, high viscosity, and thermal stability, and oxydiesel has issues related to lower lubricity, corrosion, and high vapor pressure. For example, the lower lubricity of oxydiesel, in excess of 5% ethanol, has shown to contribute to abrasive wear and cavitation in high-pressure fuel injectors in durability testing. Long-term stability of water/diesel emulsions is considered a barrier, as is the durability of fuel-injection-system components.

Gaseous fuels present additional barriers that require a significantly different approach. Their use will require a major redesign of the basic engine to address such issues as how to ignite the fuel (either by using an ignition system or a micro-pilot diesel injection).



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