As for the portion of the law regarding vehicles, it was implemented for the sole purpose of preventing (road hunting).
Pa has millions of acres of public access land, much of it in very remote areas. There are many miles of roads including dirt mountain roads thruout the region.
It was and frankly still is to some degree very possible that you would encounter a vehicle moving very slowly along with the occupants looking for game.
Many times they wont even pull over to permit another vehicle to pass them. And of coarse you can leave it to your imagination as to how they might shoot should they see something.
Very popular method during the (ahem) Elk hunt.
However you can take a position or stand along a road and shoot from it.
In some areas, long range hunters will be set up on the shoulder of the road, as a rule dirt mountain roads, with a bench having a gun sitting on it and a group of hunters glassing across the valley with tripod mounted optics.
We do likewise from the front yard of our camp, and shoot across 2 paved roads while doing so. And weve been doing it very openly for about 50 years.
And were not the only ones doing it in that area.