Sam Schwartz, a.k.a. Gridlock Sam," is one of the leading transportation experts in the United States today. He served as New York City's traffic commissioner and the New York City Department of Transportation's chief engineer. Schwartz currently runs Sam Schwartz Engineering and is a columnist at the New York Daily News. He has been profiled by the New Yorker, New York Times, and many other national publications. Schwartz lives in New York City. Follow him @GridlockSam.William Rosen is a former editor and publisher at Macmillan, Simon & Schuster, and The Free Press. He has contributed to The Wall Street Journal, The American Interest, Lapham's Quarterly, The New Atlantic, The Washington Post Book World, Bloomberg, and Smithsonian's Echoes, and is the author of Justinian's Flea: The First Great Plague and the End of the Roman Empire (Viking, 2007), The Most Powerful Idea in the World: A Story of Steam, Industry, and Invention (Random House, 2010) and The Third Horseman: Climate Change and the Great Famine of the 14th Century (Viking, 2014).