Emission Facts

Control of Emissions from 

Idling Locomotives

EPA-420-F-13-050, December 2013 

Supersedes EPA-420-F-08-014

Office of Transportation and Air Quality

I

n 2008, The U.S. Environmental Protection Agency (EPA) 

adopted new more stringent emissions standards and mandated 

the application of idle-emission controls on newly manufactured and 

remanufactured locomotives. This fact sheet provides technical background on the issue of locomotive idling and describes what EPA is 

doing to reduce emissions from this source.

Why do railroads allow locomotives to idle?

During normal railroad operations, locomotives sometimes must wait for freight 

cars to be switched and/or picked up, for another train to clear track on which the 

locomotive is to proceed, or for mechanical service. Historically, locomotives have 

been left idling while they are waiting. In some cases, there are practical or safety 

reasons why locomotives need to be left idling. In other cases, locomotive operators 

might simply idle the engines due to custom, habit, or misunderstandings about 

diesel engines. As we describe in this fact sheet, EPA is working to address all of 

these causes.

The reasons why current locomotives may need to be left idling can be technological 

or related to worker and passenger needs. First, diesel engines can be difficult to 

start in extremely cold temperatures, especially larger diesel engines such as those 

used in locomotives. Also, locomotive engines are typically designed to use water 

without antifreeze because water is more efficient at cooling the engine. However, 

the water can freeze in cold weather and crack the engine block. As a result, shutting 

locomotives off in cold weather has historically been avoided as much as possible.

Locomotive engines may also need to idle in order to maintain critical functions 

such as air pressure for the braking and starting systems and battery charge. 

Maintaining air pressure for braking is especially important since it can directly affect 

safety. Finally, in some cases, locomotives will idle to supply air-conditioning or heat 

to its crew and/or passengers, in part to comply with regulations and contractual 

requirements related to working conditions for the crew. (Note that the requirements 

related to working conditions are not regulated by EPA).
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Control of Emissions from Idling Locomotives 2

What is EPA doing to control idle emissions from locomotives?

EPA is working hard to reduce emissions from locomotives, both while they are pulling freight 

and while they are idling. However, the Clean Air Act does not give EPA unlimited ability to 

regulate locomotives. Section 213(a)(5) and related provisions provide EPA the authority to 

establish emission standards for newly manufactured and remanufactured locomotives, as well 

as to prohibit railroads or anyone else from tampering with emission controls. For locomotives 

not yet required to use the idle reduction technologies, the Clean Air Act provisions do not 

appear to provide EPA with particular authority to prevent railroads from allowing them to idle. 

Thus, as described below, EPA’s regulatory efforts to reduce emissions from idling locomotives 

focus on requiring the application of automatic idle reduction technologies to the locomotives 

themselves rather than directly regulating when railroads may allow locomotives to idle.

EPA’s 2008 rulemaking represents an important step in its efforts to reduce emissions from idling 

locomotives, which began in 1998, when EPA finalized emission standards for locomotives 

that provided significant emission reductions for all types of operation. Those initial standards 

went into effect in 2000. In addition to applying to all newly manufactured locomotives, the 

standards also require most existing locomotives be retrofitted with emissions controls when 

they are remanufactured. (This generally happens every five to 15 years, depending on the 

locomotive). These retrofit requirements have already begun reducing emissions from existing 

locomotives. Note that by requiring overall reductions in emissions, the requirements have led 

to locomotive exhaust being cleaner when a locomotive is idling, and will continue to make 

them even cleaner in the future.

In our 2008 rulemaking we adopted new requirements to further reduce emissions from idling 

locomotives by requiring technology that reduces the amount of time a locomotive spends idling 

and applying tighter emission standards to new locomotives generally. EPA is requiring that all 

newly manufactured and nearly all remanufactured locomotives be equipped with idle reduction 

technology that will automatically shut locomotives down if they are left idling unnecessarily. 

While such devices cannot eliminate all idling, they can reduce most unnecessary idling. These 

automatic controls offer more opportunities for a locomotive to be shut down by monitoring 

multiple critical system parameters to determine when it is safe to shut down a locomotive, 

relieving crews that may not have the manpower to monitor all of these parameters. In the 

field, these devices have proven themselves to be safe, reliable and extremely cost effective by 

providing reduced fuel consumption that can pay for the equipment in short order. We believe 

the cost savings associated with these devices will provide significant incentives for railroads to 

fully utilize this equipment.

Our regulations also include a rigorous emission testing program to make sure locomotives 

comply with our emission standards for their operational life. Our complete program will reduce 

NOx, HC, and PM emissions by about 90 percent. These standards will also significantly reduce 

smoke emissions and exhaust odors.

In designing this locomotive emission-control program, we established several provisions to 

ensure that emissions are reduced at all operating conditions, including while idling. First, 

we require that most locomotives comply with the emission standards over two different duty 

cycles: a high-power cycle that represents cross-country operation and a low-power cycle that 
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Control of Emissions from Idling Locomotives 3

represents freightyard operation. To comply with these requirements, locomotive manufacturers 

need to reduce emissions for all power levels from idle to full power. We also require railroads 

to improve their maintenance practices so that when locomotives are idling, their emissions 

are kept as low as would be expected from a brand new locomotive. Finally, we require that 

malfunctioning idle reduction equipment be repaired in a timely manner.

When will these mandatory emission reductions occur?

Emission standards and other requirements began reducing idle emissions as early as 2000. 

However, because it is common for locomotives to remain in service for as long as 50 years, 

the number of new ultralow-emission locomotives in a railroad’s fleet will be small during 

the start of this program. Therefore, we have designed other parts of our program to achieve 

more immediate reductions, such as the requirement that older locomotives be retrofitted 

with emission controls when they are remanufactured and provisions that require the use of 

automatic engine-shutdown features. Even so, it may take several years before these regulatory 

improvements approach full effectiveness as the fleet turns over from older locomotives to new 

less polluting locomotives.

What are railroads doing to control idle emissions from locomotives?

EPA has been working with the nation’s major railroads to implement voluntary efforts to 

reduce idle emissions beyond the mandated reductions. All Class I railroads have joined the 

SmartWay Transport Program: CSX Transportation, Norfolk Southern, Canadian National 

Railway, BNSF Railway Co., Canadian Pacific Railway, Kansas City Southern Railway, and 

Union Pacific Railroad Co. Reducing idling is one way these companies can improve overall 

efficiency and reduce fuel costs. They can accomplish this through a variety of technologies and 

strategies, including automatic engine stop-start systems, auxiliary power units or diesel-driven 

heating systems, electrical shorepower connections, and company idle-shutdown policies.

What can I do about locomotives idling in my neighborhood?

You should first contact the local railroad facility and ask about its operating practices, including 

the shutdown policy. If they are unable to help you, you might want to contact the corporate 

headquarters. Addresses and phone numbers for the major railroads are listed below. 

BNSF Railway CN (includes Canadian National Railway

and its U.S. operating sumsidiaries,

including Grand Trunk Western, Illinois

Central and Wisconsin Central).

2650 Lou Menk Dr. 935 de La Gauchetier St. W.

Fort Worth, TX 76131-830 Montreal, Quebec H3B2M9

800-795-2673 Canada

888-888-5909
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Control of Emissions from Idling Locomotives 4

Canadian Pacific Railway (Includes SOO

lines)

CSX Transportation

501 Marquette Ave. 500 Water St.

Minneapolis, MN 55402 Jacksonville, FL 32202

1-800-776-7912 904-359-3100

Kansas City Southern Railway Company Norfolk Southern Corp.

PO Box 219335 3 Commercial Pl.

Kansas City, MO 64121-9335 Norfolk, VA 23510-2191

816-983-1303 757-629-2600

Union Pacific Railroad

1400 Douglas St.

Omaha, NE 68179

888-877-7267

For More Information

You can access documents related to our regulation of locomotives on EPA’s Office of 

Transportation and Air Quality Web site at: 

www.epa.gov/otaq/locomotives.htm

Documents related to EPA’s voluntary idle-reduction programs are available at: 

www.epa.gov/smartway/technology/idling.htm

For further information, please contact us at:

Contact for Regulatory Programs Contact for Voluntary Programs

Assessment and Standards Division SmartWay Transport Partnership

U.S. EPA U.S. EPA

2000 Traverwood Drive 2000 Traverwood Drive

Ann Arbor, MI 48105 Ann Arbor, MI 48105

734-214-4636 734-214-4767

smartway_transport@epa.gov