8.3 EPA-developed estimates
EPA’s 2023 Class I rail emissions were developed using confidential line-haul activity data, in millions of gross ton (MGT) route miles per link, from the Federal Railroad Administration (FRA) for 2022 (the latest available at the time of development). 2023 rail fuel consumption index values were used to allocate each Class 1 railroad’s fuel use to links based on MGT. The Association of American Railroads (AAR) provided EPA with locomotive fleet mix information for 2023 for emission factor application. EPA then developed county-level emission summaries.
For Class II and III rail lines, location data is available online as part of Bureau of Transportation Statistics’ National Transportation Atlas Database (NTAD). Detailed documentation methodology for this work is available in the 2023_NEI_Rail_Feb_2_2026.pdf on the 2023 Supporting data FTP site.
8.3.1 Hazardous Air Pollutant Emissions Estimates
HAP emissions were estimated by applying speciation profiles to the VOC or PM estimates. These “HAP fractions” were updated for the 2017 NEI. These profiles are posted in a workbook on the 2017 Supplemental data FTP site.
8.3.2 Qualtity assurance
EPA and agency-submitted values were compared to find instances where point and nonpoint rail yard SCCs may duplicate. This occurs when agencies submitted nonpoint in the same counties where EPA had point yards. In this case, where rail yard point locations existed within the county, SLT county-level emissions were reassigned to yards to avoid double counting point and county emissions estimates.