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47 CHAPTER 6 DATA LIMITATIONS The following data limitations were identified during the GES data files could provide additional refinement of preparation of this synthesis: these data. Economic and financial data often are limited. For the trucking industry, a key source is the Motor Carrier MCMIS provides only limited data on intrastate firms. Annual Report, which is derived from U.S. DOT filings This reporting method means, for example, that school from for-hire carriers with more than $3 million in annual bus contractors that operate intrastate only, of which revenue. Although this information is very detailed, it there may be a significant number, are not fully reported may not accurately represent the financial and operating by MCMIS. While industry associations provide esti- profiles of small trucking operators and private opera- mates of this missing information through surveys, tors. Data on operating ratios, while available for the their data may not be comprehensive. trucking and motorcoach industry through the Bureau of NHTSA reports injuries and crashes in the National Transportation Statistics, are not reported for school bus Automotive Sampling System's General Estimates Sys- operators (only approximately one-third of which are tem (NASS GES) for the aggregate category of "buses." for-hire contractors). Operating costs per mile also are As a result, statistics on bus-related incidents include not readily available for the school bus industry. motorcoaches, school buses, and transit buses. Because The definition of a school bus varies from state to state NHTSA does report school bus-related incidents sepa- and is sometimes based on function and sometimes rately, a combined estimate of transit bus and motor- based on body type. coach injuries and crashes can be obtained by subtract- Historical vehicle-miles traveled data for motorcoaches ing the school bus data. and school buses are not readily available. For school bus statistics, NHTSA does not distinguish Little data exist on motorcoach and school bus driver between publicly owned school buses and privately schedules and hours worked. Specifically, industry asso- owned school buses. There is also no distinction between ciations do not collect timesheet or payroll data that school bus body types being used to transport pupils would make it possible to identify the most common and non-school buses used as school buses in the pub- driver shifts and the percentage of drivers that work lished statistics. Further analysis of the source NASS- these shifts.