When you have a little one potty training, it can make road trips challenging. A child that is still learning to use the potty, doesn't give you much time between letting you know they have to "go" and actually going. You can't ask a potty training child: "Can you hold it until I find somewhere to stop?".
The solution to this problem - keep a potty in your vehicle! I don't mean install a toilet in your van but, store a potty training seat in your trunk. That way you don't have to have your child hold it until you find a rest stop or restaurant. You can pull over into a safe area and bring the potty seat out for your child to use. I leave a space in the back of my van for our potty seat. This way my kids still have some kind of privacy and are not exposed to the weather.
If you are limited on space for storing a potty seat, there are collapsible potty seats you can purchase online.