The Routes Not Built discusses the unrealized plans to extend New York City’s subway and commuter rail system beyond the limits of the system as it now exists. It examines the reasons why the transit system did not expand and the people who played a role in the planning process. Emphasis is given to several proposes lines in particular and the impact that those plans had on growth and development of the areas that they would have served. Maps diagramming some of these lines are included. The Routes Not Taken also looks at how the subway and rail system has actually contracted in size, rather than expanded over the past 75 years through the elimination of a number of elevated lines without the construction of underground lines to replace them and the closure of other lines.