The directions for this loop are difficult to explain, and as such I recommend getting directions at the bike shop located in a shopping center in Haleiwa. We parked at the bike shop, rode out Farrington Hwy for about 10 miles, then made a left on Mokuleia Access Road (it is a paved, gated road). If you reach the airport, you have gone too far! You can also park at the gate (to shave 20 road miles off this ride) but you might find your car windows broken upon your return!
Excellent trails for running.