Okay-playing devils advocate. I know lots of parents that cut off the travel at around 6 hours (or less) and, if the student is not paying for college themselves–I think it is well within their rights to do so.
You may be overlooking that even if you can fly/pay for the flights, etc going to a school that is not “drivable” adds a whole host of additional work for the REST of the family (moving in, coordinating flights/pick ups from the airport, what happens if you get sick/injured and need a family member, etc). Might be worth it if the opportunity is amazing (for instance, traveling 12 hours to attend Yale:-).
I think the problem here is that maybe they agreed to let you look when they possibly had no intention of letting you choose a school 12 hours away. If Alabama offers something significantly different than Iowa State (I am not that familiar with either, so maybe there is something I am overlooking) that may be the best angle to take–but on the surface there may not be differences that are significant enough for your parents. If your parents are paying for college-and you don’t think they are going to change their mind, my advice would be to start embracing Iowa State.