Schwartz was educated at Brooklyn College (BS in Physics) and the University of Pennsylvania (MSCE) and first worked as a New York City cabbie before being hired by the City of New York in 1971. He served as NYC Traffic Commissioner from 1982 to 1986, and when the traffic department became subsumed by the Department of Transportation he held the second-in-command post of First Deputy Commissioner and Chief Engineer from 1986-1990. While employed with the city, he attempted to introduce bicycle lanes and public plazas. They were vetoed at the last minute by then-mayor John Lindsay. He earned the nickname Gridlock Sam during the 1980 transit strike when he developed a series of transportation contingency plans, called the Grid-Lock Prevention Program.

After he left the city government around 1996, he started his own firm. He writes columns for New York City's Daily News, lower Manhattan’s Downtown Express, The Queens Chronicle, and in the Yiddish News Report as Gridlock Shmuel. He also tweets, and blogs for the Public Broadcasting Service and Engineering News-Record.