Apologies, I am only 20 pages into this thread so probably these ideas have all been covered. I only recently discovered WebSleuths and looked into this thread because I have lived in Falmouth and also near Richmond, all decades ago.
I am reading over and over again AH was walking north in the south bound lane of I-295 or walking south in the north bound lane. IMO nobody would walk away from Portland if their intention was to get gas or to get help for a disabled vehicle. I don't believe any report that says AH was walking away from Portland.
If she was wearing black hat, coat, pants, etc nobody would have seen her at 6:30 am. Sunrise is 6:47 am on November 24. It was dark.
Related topic, if a witness says s/he saw AH between 6:30 am and 7:30 am that is very easy to pin down. 6:30 am is dark, 7:30 am is light. A credible witness would be able to tell if it was dark outside or light.
If she was walking down the highway in that area everyone would have paid attention, it is so far from normal to see a pedestrian there I can't put it into words.
From what I have read so far too much credence is given to the "hundreds of cars would have seen her" at 6:30 a.m. I looked at the camera on I 295 in Falmouth at Mile Marker 9, here:
https://www.maine.gov/mdot/maps/cameras/VC0091.jpg
Looking at the camera today, 3/16/2020, I would say the highway had zero cars in view 10% of the time I looked. At that particular stretch of road you cannot see the southbound lanes from the northbound lanes and vice versa. Traffic at 6:30 am on that highway would be busy, I agree, but would be predominantly people driving south into Portland to go to work. If you google Maine DOT plans on I-295 upgrade you will see Maine state's own statistics say at 7am traffic northbound is about 1/4 of average traffic volumes. Subtract some large portion of normal traffic due to it being Thanksgiving week, I could see AH walking along the highway without being seen. If anything related to this case really has anything to do with the reported 6:30am that day, which I find suspicious.
My last point is if AH wanted to do harm to herself that bridge on I295 over the Presumpscot River is a terrible choice. I understand people in that situation do not make rational decisions, but honestly if you drove from Richmond, ME to Portland, ME to Brunswick, ME as I think might have been the case it is hard for me to imagine a lower bridge over shallower water than that one. I'm not sure at high tide the water would be above her head. If she was home in Richmond she had a higher bridge over deeper, colder water at her doorstep. If she left Portland that morning she had already gone over higher bridges over deeper water. If she was driving to work in Brunswick she has some great choices of high bridges to jump off into the bigger, swifter Androscoggin River.
I'll keep reading here so please apologize what has already been covered.