Methodology for Measuring Access to Transportation in Rural Areas

The analysis employs a four-step GIS analysis:
1.            collection of intercity air, bus, ferry, and rail terminals;
2.            identification of areas comprising "rural America";
3.            identification of intercity facilities serving each area comprising rural America; and
4.            determining the total population served from areas with service to one or more intercity facilities.
  • Airports: Airports for 2006, 2012, and 2018 are those listed as having commercial service in the Federal Aviation Administration's (FAA's) Airport enplanement (passenger boarding) data and had scheduled passenger boardings per BTS' Office of Airline Administration airport summary T-3 data in the respective year. Large airports in the analysis refer to those with at least 0.25 percent of total passenger boardings in the U.S. in a year. FAA specifies these as large and medium airports in their enplanement data. 
  • Intercity bus stops: Intercity bus stops for 2006 came primarily from personal communication with Greyhound and Amtrak prior to the Bureau of Transportation Statistics' (BTS') June 2005 Rural Scheduled Intercity Transportation and the U.S. Rural Population report [1]. For this analysis, BTS reviewed the list of intercity bus stops and compared it to those listed in Russell’s Official National Motor Coach Guide (a national guide providing schedule and timetable information for intercity bus service in the U.S.) to create a comprehensive list of intercity bus stops as of December 2006. Intercity bus stops for 2012 and 2018 came from BTS' Intermodal Passenger Connectivity Database (IPCD), as of 2012 and 2018 respectively. BTS collected intercity bus facility information from Greyhound Lines, other national providers, and regional providers, such as those operated by State governments with funds from the Federal Transit Administration Section 5311(f) formula grants program (listed in the Russell's Guide) as well as from discount bus providers such as Megabus. The intercity bus data collection for 2012 and 2018 occurred during the course of those years without a specific reference month. For all years, the analysis includes only intercity buses with scheduled service and does not include charter buses or commuter buses.
  • Intercity rail facilities: Intercity rail facilities for 2006 are those used in BTS' February 2011 U.S. Rural Population and Scheduled Intercity Transportation in 2010 report [2]. For 2012 and 2018, intercity rail facilities came from BTS' IPCD for those years. They include Amtrak and Alaska rail facilities with scheduled service.
A rural area is a Census block group with its centroid outside of the area defined by the U.S. Census Bureau as an urbanized area or urban cluster. A Census block group is a cluster of Census blocks having the same first digit of their four-digit identifying numbers within a Census tract. Urbanized areas are towns, cities, or other places, or more than one contiguous place, with a population of 50,000 or more. Urbanized areas generally, but not always, are located around large cities. Urban clusters are places of 2,500 to 50,000 lying outside of urbanized areas. These adjacent communities are considered to be urban in character even though they often may be located far from a major metropolitan area and thus may be considered by some people as rural. As there is no clear indicator as to which urban clusters may be considered rural, all urban clusters are treated as urban in the analysis.
The Census Bureau updates Census block groups and urbanized areas during the decennial Census. BTS used the 2000 boundaries in conjunction with the 2006 intercity transportation facilities and the 2010 boundaries in conjunction with the 2012 and 2018 intercity transportation facilities. The vintage of the boundaries match those used in the population data.
A Census block group identified as rural has access to intercity transportation if its centroid lies within a 25-mile radius around a small- or non-hub airport, bus stop, or intercity rail facility or within a 75-mile radius around a medium- or large-hub airport [3]. BTS used these parameters in the previous reports and they are consist with the distance used in other studies [4]. BTS determined the size of airports from FAA's enplanement data for 2006, 2012, and 2018 respectively.  
Population data come from Census. BTS used Census 2000 SF 1 population data to determine the population with access in 2006, Census 2010 data to determine the population with access in 2012, and American Community Survey data for 2014-2018 (the 2018 5 year estimates) to determine the population with access in 2018. For block groups identified as rural, BTS summed the population data to county level to estimate the total rural population (see figure). In each county, an airport, intercity bus stop, and/or intercity rail facility were within the predetermined distance from the centroid of each block group identified as rural. For those within the predetermined distance, BTS summed the population data to county level to estimate the rural population with access to the transportation mode(s). BTS included facilities outside of the county itself in measuring access.
For all facilities, BTS made no adjustment to coverage areas to account for natural boundaries such as lakes, deserts, mountains, bays, etc., which may significantly increase the distance between a block group and the facility when traveling along the transportation network.
The interactive map shows the 2018 Census county boundaries. For counties that did not exist in 2006 or 2012 or experienced significant boundary changes, the map shows only the 2018 data. 
Figure 1: Example of How Intercity Transportation Coverage is Determined for a Rural Area
Defining rural area with access
Interactive map showing access to intercity transportation in rural areas. Data on Access to Intercity Transportation in Rural Areas by County and Intercity Transportation Facilities (rural and urban) are available. For any questions or comments, please contact Theresa Firestine.
Previous reports on access to intercity transportation in rural areas:

[3] The Federal Aviation Administration designates airports by their percentage of annual passenger boardings. Large hubs account for 1 percent or more, medium for 0.25 to 0.99 percent, small for 0.05 to 0.24 percent, and non-hub as at least 2,500 boardings but less than 0.05 percent. See:

[4] See: B.D. Spear and R.W. Weil, "Access to Intercity Transportation Services from Small Communities: A Geospatial Analysis," Transportation Research Record 1666 (Washington, DC: Transportation Research Board, 1999).
Bureau of Transportation Statistics
The Bureau of Transportation Statistics, part of the U.S. Department of Transportation, is the preeminent source of statistics on commercial aviation, multimodal freight activity, and transportation economics, and provides context to decision makers and the public for understanding statistics on transportation.