But likely she would have wanted to travel westward from the bridge (towards the central part of the UVA campus, JMU or Roanoke); to turn around and go back into Lannigan Field would be eastward. If she knew & trusted the driver; however, she might have jumped into the vehicle.
I think that from the Copeley Road bridge, the central part of UVa grounds would be east and a bit south, JMU would be north and west, and Roanoke would be south and west, but I also think we are in agreement here, and in fact a few points about this have confused me since the first hitchhiking reports.
If MH was hitchhiking on Copeley Road Bridge, I assume, though it has never been stated, that she was doing so from the side of the bridge that has a sidewalk (only one side does). That would have meant that she had crossed Copeley Road from Lannigan, back to the UHall side of Copeley, and then anyone driving by in the right hand lane would have been heading back toward JPJ and
away from Ivy Road, I-64, Crozet, Blacksburg, or Roanoke, and only circuitously toward downtown Charlottesville or central UVa grounds (but conceivably toward Harrisonburg or up 29-N, albeit cutting through UVa grounds to do so...which, admittedly, there are reasons to do.) If a car picked her up going in this direction, the Lannigan field lot either would have been immediately or shortly ahead on the left, for purse tossing possibilities.
If, on the other hand, she left Lannigan, and tried to hitchhike from that side of Copeley Road (i.e., the one without the sidewalk), then someone coming past in the right lane would have quickly reached Ivy Road, with a right turn taking one out of town toward I-64, and 29-S fairly easily, which would be consistent with getting to Roanoke, Blacksburg, Crozet, and one way to get to Harrisonburg.
Turning left at the Copeley/Ivy intersection would send one along the north border of main UVa grounds, past the "corner district," the train station, and the bus station, to downtown Charlottesville (and the downtown mall and the Omni hotel).
Same thing if she made it all the way to the Copeley/Ivy Road intersection before getting in a vehicle, though there are no confirmed reports of that. How her purse ended up in Lannigan is tougher in this scenario, unless she just dropped/forgot/left it before hitchhiking.
So if it was someone MH knew or kind of knew or wanted to meet (i.e., a known commodity as opposed to completely random), it makes sense that they would be driving on Copeley where the sidewalk is (perhaps from the Emmet/Ivy Parking Garage, but possibly many other places), and that MH stuck out her thumb only after seeing her ride.
But...while there are apparently reports of MH hitchhiking, there are apparently no reports that she got into a car. So, if she was only holding out her thumb once she saw a ride she recognized, wouldn't the witness(es) who reported her hitching have seen her getting into the recognized-by-MH car? Since they didn't, it could be that she was really and truly hitchhiking in the "looking for a random ride going my way" sense of the word.