- Airports: Total number of airports. Runways must be useable, but may be unpaved. May not have facilities for refuelling, maintenance, or air traffic control.
- Commute > Distance: Distance. Based on 0-50 contributions for Argentina, Armenia, Austria and 63 more countries and 50-100 contributions for Australia, Brazil, Germany and 5 more countries and over 100 contributions for Canada, India, and United States. The surveys were conducted by numbeo.com from January, 2011 to February, 2014. See this sample survey for the United States, respondents were asked "Distance".
- Gross value added by transport, storage and communication: Gross Value Added by Kind of Economic Activity at current prices - US dollars.
- Highways > Total > Per capita: total length of the highway system Per capita figures expressed per 1,000 population.
- Motor vehicles > Per 1,000 people: Motor vehicles include cars, buses, and freight vehicles but do not include two-wheelers. Population refers to midyear population in the year for which data are available."
- Passenger cars > Per 1,000 people: Passenger cars refer to road motor vehicles, other than two-wheelers, intended for the carriage of passengers and designed to seat no more than nine people (including the driver)."
- Ports and terminals: This entry lists major ports and terminals primarily on the basis of the amount of cargo tonnage shipped through the facilities on an annual basis. In some instances, the number of containers handled or ship visits were also considered.
- Rail > Railway length: Railway length in kilometers.
Road > Motor vehicles per 1000 people:
Motor vehicles per 1000 people.
No date was available from the Wikipedia article, so we used the date of retrieval.
- Road > Motorway density: Meters of motorway per square kilometer.
- Road > Motorway length: Total network length of all motorways in km.
- Road density > Km of road per 100 sq. km of land area: Road density is the ratio of the length of the country's total road network to the country's land area. The road network includes all roads in the country: motorways, highways, main or national roads, secondary or regional roads, and other urban and rural roads."
- Road network length > Km: Length of road network in kilometers in European Union countries.
- Roads > Passenger cars > Per 1,000 people: Passenger cars (per 1,000 people). Passenger cars refer to road motor vehicles, other than two-wheelers, intended for the carriage of passengers and designed to seat no more than nine people (including the driver).
- Vehicles > Per km of road: Vehicles per kilometer of road include cars, buses, and freight vehicles but do not include two-wheelers. Roads refer to motorways, highways, main or national roads, secondary or regional roads, and other roads. A motorway is a road specially designed and built for motor traffic that separates the traffic flowing in opposite directions."
SOURCES: CIA World Factbooks 18 December 2003 to 28 March 2011; traffic; United Nations Statistics Division; All CIA World Factbooks 18 December 2003 to 18 December 2008; International Road Federation, World Road Statistics and data files.; Wikipedia: List of countries by rail transport network size (Long List); Wikipedia: List of countries by vehicles per capita; https://www.cia.gov/library/publications/the-world-factbook/fields/2085.html, Roadways.; International Road Federation, World Road Statistics and electronic files, except where noted.