Thanks for the replies;
Firstly, there's no safer route - the "4-lane" arterial is actually a 55mph 2-lane rural route. I don't really see anything I can do to change my dad's mind - he hasn't ridden in decades and I don't see him riding on a rural road. And its kind of hard to convince a rational person that riding 15mph on a bike is safer on an unlit rural road than 45mph (traffic speed) in a car. I'm not going to disobey him, though I did ride around my neighborhood this morning. I'm just waiting for college right now, which fortunately is less than a year away-They've already told me that they don't have a problem with me riding when the speed differential is 15mph or less.
As for the car driving thing, my parents would, at least initially, subsidize most of the costs. I just don't see the point - the only currently available parking lot is a 15-minute walk from the front of the school (with a 15-minute drive assuming traffic), at which point I might as well have made the 50-minute walk home (riding took about 15-20 minutes, and I could park adjacent to the school doorway).