Amid all the debate about the risk of coal trains spreading coal dust into areas near the railroad tracks, it’s often forgotten that the subject is controversial even within the industry. How to control coal dust—or whether it can be done at all to a meaningful degree—has been the subject of a long-running dispute between those who ship the coal and those who carry it. The coal companies or utilities that ship the coal are on one side and the railroads that carry it are on the other.

The controversy developed originally not because either side was concerned about the spread of coal dust into neighboring communities or rivers, but because coal dust accumulation had become so severe in places that it actually destabilized tracks, resulting in derailments or trackside fires. In response, the railways began levying fees on the coal shippers to cover the costs of treating the coal with a chemical spray designed to reduce dust emissions. The coal shippers objected, arguing that the fee was unfair and that the coal dust control techniques are ineffective.

The result was a years-long battle before a federal regulatory agency, the US Surface Transportation Board (STB). It was finally resolved in December 2013 when the STB ruled mostly in favor of the railways—the government denied the fee, but instead allowed the railways to require coal shippers to undertake the dust-reduction techniques the railways wanted. (The ruling is here.) The legal arcana may be of little interest outside law firms, but the research results that supported the decision are relevant to everyone with a stake in the coal exports debate.

The STB relied on the findings of a seven-month experiment called the Super Trial designed to answer some of the persistent questions about how effective coal dust suppression techniques really are. Although the government concluded that it is possible for shippers to substantially reduce coal dust, the research findings also leave open several major worries, among them:

  • Coal dust from empty railcars, which may emit as much dust as loaded cars and which are never treated to reduce dust.
  • Coal dust reduction techniques may not be effective at high speeds or over long distances.
  • The studies tell us little about the extent of very small particle emissions, which may be the most risky to human health.
  • Much of the methodology and results are proprietary, making them hard to evaluate.

It’s worth taking a closer look at the STB case because the answers can help us glean important information about what large-scale rail shipping would mean for coal dust in the Pacific Northwest.

The Super Trial

In the Super Trial, two major coal-hauling railways, BNSF and Union Pacific, conducted an experiment between March and September 2010 in the Powder River Valley, the origin of virtually all the coal intended for export from planned new terminals in the Northwest. Analysts for the railways treated 1,633 trains with “topper agents,” which they applied either before the coal was loaded into railcars or to the surface of the coal after loading. They then deployed two different techniques for measuring coal dust: passive dust collection on the railcars and trackside monitors. On 115 trains, they used passive dust collectors, designed to capture particles larger than approximately 120 microns. On the remaining 1,518 trains, they measured coal dust escape using trackside monitors placed at milepost 90.7 and at milepost 558.2. Unfortunately, the results in the publicly available documents are very incomplete and are not expressed in standard terms so they cannot be compared with published reports from other studies.

Based on the results of the Super Trial, the STB ruled that coal shippers could be required to reduce dust by means of two methods: shaping the coal in railcars into a bread loaf shape and applying topical agents of selected chemicals over the surface of the coal after loading it.

Not everyone was convinced that the Super Trial findings were definitive though. In a legal and technical argument an array of coal shippers complained about the results for a range of reasons. They argued, in short, that it is not possible to substantially reduce coal dust emissions, at least not using the railways’ preferred techniques, which were evaluated in the Super Trial. The STB evaluated the coal shippers’ arguments together with responses by BNSF Railway and, ultimately, sided with the railways on every issue.

Yet we think that a few of the coal shippers’ complaints may be at least partially legitimate and potentially concerning for Northwest communities. We examine those issues here.

Not real world conditions

Coal train and coal loader

Coal train and coal loader Image by Beyond Coal and Gas used under CC BY-NC 2.0

Arkansas Electric Cooperator Corp. (AECC), acting as a lead representative for the coal shippers, claimed that the chemical topper agents are far less effective than the railways allege. In particular, they argued that the Super Trial ignored the eﬀects of weather (including cold, wind, and rain) on the application, curing process, and overall eﬀectiveness of the chemical topper agents; ignored the effect of train speed on coal dust loss; and ignored the effect of distance because the tests only considered coal dust loss over a limited distance. They argued further that the results do not show that the topper agents will reduce loss over the entire trip and, in fact, may actually lead to greater losses later in the trip.

BNSF replied that the Super Trial included trains running at a range of wind speeds. Although they declined to reveal data about wind, the railway claimed there was no diminution of dust emission for trains running at less than 40 mph. Moreover, said BNSF, since the relevant measure was dust emission from treated cars relative to that on untreated cars on the same train, weather and speed are irrelevant.

BNSF did not, apparently, respond to the claim that topper agents might lose their effectiveness over time or distance and potentially result in greater emissions later on in the trip—a potentially big factor for the Northwest, which is relatively far from the mines where the topper agents are applied. In fact, according to a comprehensive study by Environment Canada, emissions do tend to increase with distance whether or not the coal is treated with a topper agent. Just so, studies by Environment Canada and others have shown that dust emissions increase above a total wind speed (the speed of the air relative to the coal on the moving train) threshold of roughly 30 mph, though Environment Canada also reports that the issue has not been well studied.

The data don’t support the conclusion

The coal shippers claimed that the measurement system detected significant dusting from treated trains during Super Trial testing, in contradiction to the railway’s assertions that the topper agents are effective.

BNSF countered that, to the contrary, the monitoring stations showed very large reductions in dust particles. In fact, BNSF claims that the topper agent treated coal trains showed a 100 percent reduction in particle emissions at the second monitoring point. But if the monitors really did show a complete elimination of emissions, it’s actually evidence that the nonstandard parameter they used to measure those emissions deliberately excluded very small (micron size) particles, such as those from the exhaust that is always present near diesel-burning locomotives, although the trackside monitors were capable of sensing these small particles.

In our view, it is therefore not possible to evaluate the impact of the coal dust suppressants on these ﬁne particle emissions because of the limitations of the data presented by the railways. Small particles were not the focus of the Super Trial because they do not degrade railway ballast, but they may be of considerable importance to health and air quality, as well as global warming.

The data are suspect

The coal shippers questioned the competence of the consultants. AECC argues that in some instances, BNSF and its consultants actually changed the results when they believed the data were not consistent with what they expected, calling into question the validity of the results.

  • The main technical analyst for BNSF is George David Emmitt, president of Simpson Weather Associates (SWA), a scientiﬁc consulting ﬁrm that appears to be preeminent in the ﬁeld. He is a former atmospheric scientist with a distinguished research record. However, his ﬁrm has a record of maintaining data secrecy. Environment Canada researchers have also complained they were unable to view relevant measurements that SWA made in a West Virginia study. And Dr. Emmitt did not respond to our request for clariﬁcation about speciﬁc points for this article.

    The coal shippers argued further that because only 10 to 17 trains were treated with each different topper agent there is not enough data to enable statistically reliable conclusions. In addition, we are very concerned by the fact that no uncertainties or error bars are presented for any of the (meager) numerical results of the Super Trial, which is highly unsatisfactory.

    Dr. Emmitt responded to the coal shippers’ argument by saying that he did not need to conduct more tests because, when topper agents were applied, the amount of coal dust emissions varied little from train to train, whereas for untreated coal the amount of dust varied significantly. Although statistical analyses of the data were apparently presented to the relevant adjudicating bodies, they are (like most of the other data from the Super Trial) excised from the publicly available documents.

    Empty coal train

    Empty coal train Image by greatlettuce used under CC BY 2.0

    In addition to complaints raised by the AECC and the coal shippers, we note that the Super Trial study design was concerning in some other respects. For one, the results excluded data from days in which the topper application was irregular or faulty. It also did not evaluate empty coal cars, even though there is evidence that dust from empties can be as high as from full cars. Communities near railroad tracks may rightly worry because empty coal cars are never treated with any form of dust suppression.

    After reading the complaints and rejoinders, as well as the publicly-avail­able documentation on the Super Trial, our view is that the science is, for the most part, on the side of BNSF’s coal dust suppression techniques for loaded coal trains. That said, we are very concerned that many of the Super Trial results could not be measured or explained by using the documents available to the public. In addition, the apparently dominant role of one scientific consulting ﬁrm, SWA, throughout the North American railroad industry may be problematic. At minimum, it allows for a degree of secrecy in the findings that are reported to the public.

    It is probable that BNSF is doing a reasonable job in preventing coal dust from contaminating its railway infrastructure, but what the Super Trial results mean for broader impacts on communities and the environment is ambiguous at best. In fact, research soon to be published by Dan Jaffe, a University of Washington Professor of Atmospheric and Environmental Chemistry, appears to show that dust emissions from coal trains can be a significant local as well as global pollutant.


    Marcia Baker is professor emerita of Atmospheric Sciences and Earth and Space Sciences at the University of Washington.