newbie questions about the LP end

[MTVhike]

I'm just starting to explore the NP trail by starting at the LP end and going a couple of miles yesterday afternoon, and have a couple of questions:
1. The first three bridges seem to be build to support snowmobiles; is that their intent?
2. Why was the northern terminus moved? The current one is much closer to LP than the old one, which, I assume, was the one used when people would hike to the train station. After my short hike yesterday, I drove to the end of Averyville road to the PA for Pine Pond, and noticed (on my map) that I was very close to the old terminus.
Also, according to my map, the trail to Pine Pond is identified as a road (of sorts); are bicycles allowed there allowing people to tow their boats on a bike trailer?