If you're wondering why some streets are closed in the city today, it's because it's the Five Boro Bike Tour. According to Bike New York, the ride starts in Lower Manhattan and then "heads north through the heart of Manhattan to Central Park and continues on to historic Harlem and the Bronx, returning south along the East River on the FDR Drive. From there it crosses into Queens and then Brooklyn, where cyclists take over the highway before making the thrilling climb up--and down--the Verrazano-Narrows Bridge to Staten Island. The route is 42 miles, mostly flat except for the bridges." Here's a PDF from the NYPD outlining all the street closures.

Above is a cool panoramic shot of an early stretch of the tour in Manhattan byFlickr user how long it takes—check out the huge version.