Honolulu

Politicians in Washington D.C. are getting behind Honolulu's plans for a $3.7 billion light rail system, calling it the "most efficient light rail project in the country".

The blog post features a list of the top five densest cities in America, and looks at the conditions that have made them that way.

The costs of Honolulu's planned commuter rail system have been estimated at nearly $4 billion, but that price tag is expected to rise further as the system develops.