Logistics can be tricky, but there is a good chance your child is actually excited about the idea of riding a bus. My son would have loved that, at that age. Assuming, of course, it isn't with a large group of unsupervised NT kids.
If he is OK with it, let go of that worry and simply be glad you have found a school that you think he can thrive in.
_________________
Mom to an amazing young adult AS son, plus an also amazing non-AS daughter. Most likely part of the "Broader Autism Phenotype" (some traits).