The bottom to which I referred is only about a quarter mile or so, down the hill from Fielding Dr., but in a direction that Brad would probably never go. But, between his kid's preschool and the Adams, a route that he's probably taken, there's a driveway-like access to a television tower surrounded by woods; I assume that he probably takes Davis Dr. to RTP and there's still quite a bit of virginal land along that route. I think he wanted to get her out of the trunk, ASAP and he might've known about that cul-de-sac (possibly from looking for a quiet, nearby place to talk with his girlfriend) and once he came up with the jogging scenario, it simply met his needs.
ETA: You'd think that if the murder had been planned, a techie like Brad would've used Google Earth to find places to scout, where he could quickly get in and out, while leaving the body where it'd not soon be found.