For those who’d like a long run, this is a great 12 mile loop. The highlight is the run over the Cross Island Bridge, with great views of the harbor and marshes. The route starts at Shelter Cove (near the Disney Resort), and follows the main Hilton Head Rt. 278 west for 2.5 miles. It’s a commercial street, but there’s a bike lane. Turn right on Palmetto Rd. (you can run the parallel Arrow Rd. for something a bit quieter), to get to the bridge. Coming off the bridge, take Marshland Rd. east, for 4 miles. There are good marsh views in spots, shade, and a bike lane along the road. Turn right at Mathews Dr., to get back to Rt. 278.
There aren’t many options to shorten the run, since there are no roads north of the harbor other than Palmetto and Mathews. Of course, one could just park near the bridge and run over and back, for a nice run and the views.