It’s time for you to be independent. You will be alone at college. Doesn’t sound like traveling is the real issue. Are you an only child?
Do you have a relative who could join you other than your parents? I took my niece on her revisits a few years ago because her parents were not able to go.
Call the admissions office at the colleges you want to visit. They deal with parents’ concerns all the time. They may be able to provide the reassurance that your parents need. They may have someone to pick you up at the airport or train station. They may have a current student on campus to help you and someone to whom you can direct your questions. No one wants you to be “Taken” like in the movie! Ask the admissions office for help in planning your visit. I saw several students on admitted students day visits and even several who went to move in day on their own. It is a really good way to meet other students who are not being closely “supervised” by their parents. As your parents watch you doing these steps, they will feel more confident about your emerging independence. Write down all of the steps you are taking and share them with your parents to reassure them. Then they can rethink their own concept of you as an emerging young adult.