The following definitions are from the Transit Cooperative Research Program (TCRP) Report 62: Improving Public Transportation Access to Large Airports and the American Public Transportation Association (APTA), 2004 Public Transportation Fact-book to describe ground connection services at airports

Metropolitan Statistical Area: A geographic entity having a core area with a large population nucleus, plus adjacent communities with a high degree of economic and social integration with that core.

Transit Buses: These buses usually do not have luggage compartments or restroom facilities, and serve a specific intra-city or regional service area. Bus types may include electrically powered trolleybuses, dual-mode trolley buses, articulated buses, replica trolleys, or double-decked buses.

Inter-city buses: Usually with separate luggage compartments and restroom facilities and high-backed seats for use in high-speed long-distance service, and typically providing service to cities outside the metropolitan statistical area in which an airport is located.

Bus Rapid Transit: Express bus service characterized by the use of a dedicated roadway or restricted usage lanes, and a limited number of stops.

Commuter Rail: Electric or diesel propelled railway for urban passenger train service consisting of local short distance travel operating between a central city and adjacent suburbs. Service is operated on a regular basis by or under contract with a transit operator for the purpose of transporting passengers within or between urbanized areas and outlying areas. A commuter rail (CR) car is a commuter rail mode passenger car - either an un-powered passenger coach that is pulled or pushed by one or more locomotives, or a self-propelled passenger car that has an onboard power source or that draws power from overhead electric wires (i.e., METRA commuter rail train in Chicago). A locomotive is a power unit vehicle that does not carry passengers that is used to pull or push commuter rail passenger coaches.

Heavy Rail: An electric railway with the capacity for a heavy volume of traffic characterized by high speed and rapid acceleration passenger rail cars operating singly or in multi-car trains on fixed rails excluding all other vehicular and foot traffic and having an on-board operator. These transit systems (i.e., metro, subway, rapid transit, or rapid rail) are defined by their operation on a totally separated right-of-way, and use of a third rail on the ground to power the trains. Heavy rail systems require platform boarding, typically have longer distances between stations, and have a greater capacity than Light Rail systems (i.e., MTA New York City Transit heavy rail train).

Automated Guide-way: an electric railway (single or multi-car trains) of guided transit vehicles operating without an on-board crew. Service may be scheduled or in response to a passenger activated call button. An automated guide-way (AG) car is a guided passenger car operating under a fully automated system without an onboard crew (i.e., people mover), which typically operates on a loop or shuttle route within the central business district of a city. The Newark Airport Air-Train in New Jersey uses monorail technology, but is an automated guide-way since the trains do not have operators.

Monorail: An electric railway of guided transit vehicles suspended from or straddle and/or guide-way formed by a single beam, rail, or tube.

Light Rail: Usually driven by electric power taken from overhead lines, and usually, operates much, or all, of its route on non-exclusive right-of-way. A metropolitan-electric railway system characterized by its ability to operate in a variety of environments such as streets, subways, or elevated structures. Light rail systems can operate on streets with other traffic. They typically use an overhead source for their electrical power and boarding take place from the street or platforms. Light rail systems operate in both exclusive and shared right-of-way environments, and have stricter limits on their length and the frequency of service than heavy rail systems.

High Speed Rail (HSR): refers to a series of technologies involving trains traveling at top speeds of 90 to 300mph. This service may require separate, dedicated tracks and "sealed" corridors in which grade crossings have been eliminated, either through closure or through the construction of highway underpasses or overpasses.

High Speed Rail Corridor: A geographical area designated by the Federal Railroad Administration to receive specially targeted funding for highway-rail grade crossing safety improvements, and recognized as a potential center of HSR activity.