The Race Underground: Boston, New York and the Incredible Rivalry That Built America's First Subway by Doug Most

The path from horse-drawn carriages in the late nineteenth century to electric subways was not always a linear solution, nor was it easy. Relief from congestion in Boston and New York, two of the country's early-growth cities, was to be the metaphorical “light at the end of the tunnel.” It is interesting that today, any grander agenda for the expansion of subways -- or public transportation in general -- seems to have taken the back burner, superseded by Americans' love of the automobile. 

Nevertheless Doug Most's chronicle of how the subways got their start in two of the most dynamic metropolises in the United States makes for riveting and compelling reading. Highly recommended, especially for history geeks.