Can I open a sub page from my reservation form?

example for one way or round trip

I'm not sure if I understood your question, could you please take a look on the following guide and check if this is what you're looking for? 

https://www.jotform.com/help/317-Change-Thank-You-Page-URL-Based-on-a-Condition 

You may also provide us more details about what you would like to achieve, we  will be glad to help you. 

You mean a different input fields depending on which option they choose? (one way or round trip) If that's what you wanted, then that's possible through conditional logic settings. This article might give you some jumpstart.

https://www.jotform.com/help/297-Show-or-Hide-Multiple-Fields-at-Once-Using-the-Form-Collapse-Tool

Also, here's my sample form.
https://form.jotform.me/71418694997476

As you can see, it will display the field depending on your choice.