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A '''Subway''' is a Rapid Transit system that runs underground for much or all of it's route.  Subways require large populations to run efficiently and run at a "grade seperation" from other vehicles and run frequently.  This means that they exist in the largest cities.

A '''Subway''' is a Rapid Transit system that runs underground for much or all of its route.  Subways require large populations to run efficiently and run at a "grade seperation" from other vehicles and run frequently.  This means that they exist in the largest cities.

The first subway was opened in [[London]] in 1863, (where it is called the "[[Underground]]") although many more major cities now have subways systems.  The [[Boston]] subway opened in 1901 and the [[New_York_City|New York]] subway first opened in 1904.

The first subway was opened in [[London]] in 1863, (where it is called the "[[Underground]]") although many more major cities now have subways systems.  The [[Boston]] subway opened in 1901 and the [[New_York_City|New York]] subway first opened in 1904.