cdale...
When I reach that sharp left turn that goes uphill and takes me over the AMTRAK bridge, I've seen that, if I were to continue straight instead, there is a narrow dirt trail that goes somewhere unknown. I have often wondered if it leads to a point further down Neptune or somewhere in that neighborhood. However, it is always overgrown and I've never wanted to risk tick bites or getting my loaded rig stuck in the grass somewhere, so I haven't explored it. Is this the "dirt/grass right-of-way" you described that leads to Haley Crescent (which is not shown on Google Maps, from what i can see)?