The Second Avenue subway in New York City is no longer a pipe dream. One section is set to open in December 2016 and is expected to carry about 200,000 riders a day. The Second Avenue subway was first proposed in the 1920s. But over the decades, funding was derailed by the Great Depression, World War II and financial obstacles, including the 1970s recession and the costs of simply maintaining the world’s largest subway system. The Second Avenue line is the first major expansion of the New York City subway system in more than 50 years. The agency says there has never been a project this massive done in such a densely populated area. “CBS This Morning” is taking the first drone ever allowed inside the New York subway system, with an exclusive look at a vital transportation advance in New York City.