Forgive me if this question has been addressed, and please direct me to the anwser:

In the rrg: speeder spells out movement. However, under area terrain ( p. 8 and large objects (p 9), the charts list dense woods, high hedges, high dirt walls, high stone walls and buildings as impassable.

Um, what? Confused. A speeder 1 should be able to go over most of those.

Anyone care to shed light on rhis for me?

You can go over any terrain (including impassable) as long as its height does not exceed your speeder X value.