Is it possible to create an open world for transport?

I’m making a game in which truckers drive through the wastelands between settlements, fighting off raiders on wheels. I’m doing great, except creating the world.
I can’t create a map with a grid density higher than 8kx8 K. Because of this, I get either a small map that can be driven in 5 minutes, or a large map consisting of tiles the size of a parking lot.
What can be done in my case?

World composition and 8km tiles will work fine.
Maybe use the 8km format at a 4km size, or the 4km size depending on what platform you want it to run on…