For a long, straight, flat run with water views, Dune Rd. is the best bet in the Hamptons. The road runs for 14 miles, from 8.4 miles from the western end at Cupsogue Beach County Park to Shinnecock County Park West at the eastern end. The road starts 1 mile from Main St. Westhampton, and parallels the beach the whole way. The eastern end is a little more rugged, with frequent splashovers from the water, with sand in the road. Toward the western end, there are some oceanfront houses, and Cupsogue Beach County Park offers supervised swimming, recreation, and concessions. Within the park, there’s a dirt road/path that goes for 1 mile. At the eastern end, one can continue onto the Ponquogue Bridge, whose 1-mile crossing is great for running, with a sidewalk and wonderful views .
There is no sidewalk on the road, but it is untrafficked enough to be fine for running. A good starting point is Rogers Beach, which is 1 mile from Main St. in Westhampton. From there, it is 5.7 miles west to Cupsogue Beach County Park, or 8.4 miles east to Shinnecock County Park.