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Acknowledgments US Department of Transportation - BTS

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Appendix EData Source and Accuracy StatementsChapter 1 Extent, Condition, and PerformanceTABLE 1-1. System Mileage Within the United StatesHighwayThe Highway Performance Monitoring System (HPMS) is the source <strong>of</strong> road mileage data and is considered reliable.(See box 1-1 for detailed information about the HPMS.) The Federal Highway Administration (FHWA) <strong>of</strong> the U.S.<strong>Department</strong> <strong>of</strong> <strong>Transportation</strong> (<strong>US</strong>DOT) collects and reviews state-reported HPMS data for completeness,consistency, and adherence to specifications. Some inaccuracy may arise from variations across states in theiradherence to federal guidelines in the Traffic Monitoring Guide and the Highway Performance Monitoring SystemField Manual for the Continuing Analytical and Statistical Database.Beginning with the 1997 issue <strong>of</strong> Highway Statistics, FHWA instituted a new method for creating mileage-basedtables derived from the HPMS. Previously, adjustments to tables developed from sample data were made using areawidemileage information provided by states. These adjustments are now being made using universe totals from theHPMS dataset. In addition, FHWA has discontinued the process <strong>of</strong> spreading rounding and other differences acrosstable cells. Thus, users may note minor differences in table-to-table totals. FHWA considers mileage totals from tableHM-20, "Public Road Length, Miles by Functional System" to be the controlling totals should a single value berequired.Reliability may be diminished for comparisons with pre-1980 data, which were collected via different methods andspecial national studies. For instance, pre-1980 mileage data included some nonpublic roadways (95,000 miles in1979) while post-1980 data reports only public road mileage (roads or streets governed and maintained by a publicauthority and open to public travel).Class I RailThese data are from Railroad Facts, published annually by the Association <strong>of</strong> American Railroads (AAR). AAR dataare based on 100-percent reporting by Class I railroads to the Surface <strong>Transportation</strong> Board (STB) via Schedule 700<strong>of</strong> the R1 Annual Report. The STB defines Class I railroads as having operating revenues at or above a thresholdindexed to a base <strong>of</strong> $250 million (1991) and adjusted annually in concert with changes in the Railroad Freight RateIndex published by the Bureau <strong>of</strong> Labor Statistics. In 1999, the adjusted threshold for Class I railroads was $258.5million. Declassification from Class I status occurs when a railroad falls below the applicable threshold for threeconsecutive years. Although Class I railroads encompasses only 2 percent <strong>of</strong> the number <strong>of</strong> railroads in the country,they account for over 71 percent <strong>of</strong> the industry's mileage operated.To obtain railway mileage, AAR subtracts trackage rights from miles <strong>of</strong> rail traveled on line 57 in the Schedule 700report. Historical reliability may vary due to changes in the railroad industry, including bankruptcies, mergers, anddeclassification by the STB. Small data errors may also exist because <strong>of</strong> because <strong>of</strong> independent rounding <strong>of</strong> thisseries by AAR.AmtrakThese statistics originate from the Statistical Appendix to Amtrak's Annual Report. Amtrak estimates track mileagebased on point-to-point city timetables that railroad companies provide for engineers. The figures are estimates, butare considered reliable.TransitThese data are based on information in the U.S. <strong>Department</strong> <strong>of</strong> <strong>Transportation</strong>, Federal Transit Administration (FTA),National Transit Database (NTD). The legislative requirement for the NTD is found in Title 49 U.S.C. 5335(a). Transit

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