I assume you are referring to why would the murderer(s) go south, via the railbed? If so, it is entirely possible they knew the home at the end of the private drive was not occupied. That affords them relatively safe access to that property and a heavily wooded area to the southeast, culminating in a short stretch of wooded area to route 200.
That gets them away from the usual trails, the bridge, the creek, the entrance to the trails, the cemetery, all those points that seem obvious to search.
The route south through the woods gives the killer(s) immediate removal from what they may have determined to be the most likely places to be detected.
If you refer to a possible Bridge Creek escape, that would be an excellent way to escape detection, be picked up on the highway, and get out. If a killer is already wet, walking out through a stream, or in and out of a stream, would be a non issue.
carry on