My 16-year old son bikes to school most days, even though he has access to a car. It's flat here, so he doesn't have all the problems you do, but he gets his share of abuse from drivers. I second the things written by the others here. Do not let the drivers intimidate you. What oyu are doing is good in innumerable ways, and I strongly encourage you to keep it up. You'll find that the trip gets easier as you get stronger. Getting a good-quality bike also makes a huge difference. Biking early in the morning sharpens the mind for morning classes. Girls dig the quads. Keep persevering, and you will see the beneifts.