- Southern Terminus:
- Union Boulevard (CR 50) in Bay Shore
- Northern Terminus:
- Deer Park Avenue (NY 231) in North Babylon
- 4.33 miles
CR 50 is a diagonal route extending from Bay Shore to North Babylon. Third Avenue begins as a local street at Montauk Highway (NY 27A) and runs north. After a few blocks, it comes under county jurisdiction as CR 57 at Union Boulevard (CR 50). After another few blocks, CR 57 splits off to the west onto Roosevelt Street, which changes names to become Howells Road. It runs northwest to meet the service roads of Sunrise Highway (NY 27) at a circle. Shortly thereafter, it changes names to become Bay Shore Road. There is an interchange with the Southern Parkway between the Robert Moses Causeway and the Sagtikos Parkway. Bay Shore Road continues northwest to North Babylon, where it ends at Deer Park Avenue (NY 231).