All good points. But I think Diane was drunk enough, she might have set her phone down and almost instantly forgot it was there. (Does someone want to refresh my memory? Was the phone ever found? If so, where?)
The phone was found on top of the concrete abutment in the emergency lane off the Tappan Zee bridge on the Eastern side of the bridge. Diane must have just gone through the toll booth. If she was THAT drunk at that time, it would seem like a toll collector would have noticed. Although I think she used easy pass to go through the booth. If that was the case, she would have had to have crossed about 4-5 lanes of traffic (at least 2, which are cash lanes) to get to the side there. The side where she stopped is about 40 yards from the Tarrytown exit. It's right over on the right there. The thruway continues on the left. The next exit is the Saw Mill and it's kind of a tricky entrance if you're going south. Of course she ended up North of there on the Taconic. I suppose she must have gone north on the saw mill. It's winding and narrow, but the entrance north is a bit easier to navigate than the entrance to the south (the south entrance you have to make a full stop and merge into traffic that is coming out from under a bridge. It's tricky even when you're stone cold sober).
If she went north on the saw mill she was going in the wrong direction from her home, which is on long island. She should have continued on I-87 towards the bridges (Whitestone, Throg's Neck) on the east side over there. I will fully admit that the road system of parkways in NY are confusing and difficult to master. When my parents visit me (from the south), they can't believe how winding and narrow they are. And the signage stinks. I suppose she got confused.
So, going north on the saw mill would take her back toward I-87 and if she was going to long island, she should have gotten back on I-87 going east, away from the Tappan Zee. The entrance to the Taconic is just north of that exit. She would have had to have gone up the Taconic in the right direction, gotten off and turned around, going south in the northbound lane.