Information:  - The North County Transit District (NCTD) is the agency responsible for public transportation in North San Diego County, California, United States. NCTD provides 12 million passenger trips per year. NCTD's geographic area is approximately 1,020 square miles, with an approximate population of 842,000 people. NCTD is governed by a Board of Directors.  - The Coaster ( reporting mark SDNX ) is a commuter rail service that operates in the central and northern coastal regions of San Diego County , California , United States . The service is operated by TransitAmerica Services on contract with North County Transit District ( NCTD ) . The service has eight stops and operates primarily during weekday peak periods , with additional weekend and holiday service .  - A suburb is a residential area or a mixed use area, either existing as part of a city or urban area or as a separate residential community within commuting distance of a city. In most English-speaking regions, suburban areas are defined in contrast to central or inner city areas, but in Australian English and South African English, "suburb" has become largely synonymous with what is called a "neighborhood" in other countries and the term extends to inner city areas. In some areas, such as Australia, China, New Zealand, the United Kingdom, and a few U.S. states, new suburbs are routinely annexed by adjacent cities. In others, such as Arabia, Canada, France, and much of the United States, many suburbs remain separate municipalities or are governed as part of a larger local government area such as a county.  - Commuter rail, also called suburban rail, is a passenger rail transport service that primarily operates between a city centre, and the middle to outer suburbs beyond 15 km (10 miles) and commuter towns or other locations that draw large numbers of commuterspeople who travel on a daily basis. Trains operate following a schedule, at speeds varying from 50 to 200 km/h (30 to 125 mph). Distance charges or zone pricing may be used.    What is the relationship between 'coaster ' and 'rail transport'?
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