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About Clean Diesel


Rail transportation is vital to the U.S. economy. Freight train engines rely almost exclusively on diesel and haul roughly one-third of the freight in the U.S. Commuters in cities across the country rely on America’s railroads every day.

Railroad locomotives fall into three size categories:

History of the Diesel Train

Freight train engines rely almost exclusively on diesel. The first over-the-road diesel freight engines entered service in the 1930s and the number of diesel-powered trains in the U.S. surpassed 1,000 in 1940 - most for passenger service.

By the early 1950s, the number of diesel locomotives exceeded the number of steam engines. Today, the steam locomotive has faded into history while over 21,000 diesel trains are in operation nationwide.

Diesel engines have substantial economic advantages over other power sources for locomotives. Diesel's thermal efficiency is approximately four times greater than that of steam locomotives. As a result, these engines require substantially less fuel for equivalent power.

In addition, diesel locomotives accelerate quickly and run at high speeds with minimal track damage. They function with similar efficiencies as electric locomotives, but do not require the capital investments in substations and electric distribution networks.

Regulations and Standards

The diesel industry and rail manufacturers continue to invest resources and make strides toward producing the cleanest train technology possible. Diesel engine technology in railroad locomotives has advanced dramatically in recent years. Fuel-efficiency has increased 61 percent since 1980.

In 2004, the U.S. Environmental Protection Agency (EPA) released its Final Nonroad Diesel Rulethat will require train engines meet strict air quality standards. As part of this standard, trains will achieve low emissions levels that will reduce sulfur emissions by 99 percent. These fuel improvements will create immediate and significant environmental and public health benefits.

At the same time, clean rail standards will also require the use of advanced emission-control technologies similar to those already upcoming for heavy-duty diesel trucks and buses. The availability of clean non-road diesel fuel means that advanced clean diesel technology will reduce NOx and PM emissions by 90 percent in rail technologies.


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