Each school board that provides for the transportation of students pursuant to § 22.1-176 and that has established a rule, regulation, or policy to exclude certain students who reside within a certain distance from the school at which they are enrolled from accessing such transportation shall establish a process for waiving, on a case-by-case and space-available basis, such exclusion and providing transportation to any such student whose parent is unable to provide adequate transportation for his child to attend school because the parent is providing necessary medical care to another family member who resides in the same household, as evidenced by a written explanation submitted by a licensed health care provider who provides care to such family member.