The Hudson River VFR corridor is one of two pathways of airspace created by the FAA in 1971 to allow VFR traffic to operate clear of the busy Class B airspace of the New York City area. The corridor extends from the surface of the river to 1100 feet AGL with controlled airspace at 1101 feet on up. Aircraft in the corridor use a common frequency of 123.5 MHz to announce position and altitude; northbound traffic follows the Manhattan shore and southbound traffic follow the New Jersey shore. More than 200 aircraft use the corridor daily.
The other pathway is the East River VFR corridor which has been closed to aircraft unless under positive control since October 2006 following the crash that killed Yankees pitcher Cory Lidle and his flight instructor.
Source: Aviation Week & Space Technology, August 17, 2009. "Midair Mystery- Collision follows decision to fly river route; Pilots face limits on popular VFR corridor" by Frances Fiorino, p52.