The first thing I noticed was that, according to the accepted time frame (Maura leaving UMass at 4:30, getting into an accident in Haverhill at about 7:29), Maura had about 45 minutes unaccounted for. If she had driven straight from UMass to that location, she should have arrived sometime around 6:45. Of course, we know she stopped for gas somewhere along the way. And perhaps she stopped for food.
As soon as I arrived in the Haverhill area, I checked in at the Wells River Motel, dropped off most of my booze and luggage, and then drove out to the scene of the accident. It was only when I arrived that I discovered the items I had in my car matched the items found in Maura's. My bag and liquor were gone. The book was there. I started to wonder then if Maura might have already arrived at her destination before driving out to Route 112. It would explain some of the lost time. Perhaps she stopped, dropped off her stuff, then drove away, looking for a place to eat.
If that's the case, the prime suspect in her disappearance becomes whoever checked her into a her hotel (there are few in the area) or whoever she had driven up to meet (if that is what she did). Perhaps it was that person who picked her up at the scene. It would certainly go a long way toward explaining why she got in the car. It's another possibility I've thought a lot about.