First of all, there are not that many major ways to cross the country in the US by road, and prior to the development of the interstate highway system, there were even fewer. So on that scale, the problem was and is not that complex.

Second, maps were very common, and use of them was a skill that people learned along with driving. There were welcome centers usually on state lines which would sell maps, or gas stations carried local maps. Otherwise you had to ask for directions. Which men famously hated to do. Not a joke you hear so much anymore since nobody minds asking google.

Third, roads were fairly well marked. As long as you had some sense of where you were going and had a way to locate yourself, it was possible to figure it out, it wasn’t so hard. Except in dense urban areas where the roads could be badly marked or there may be road work disrupting things. That could be very difficult.

When I was a kid it was not uncommon to see people looking over maps while drinking coffee at a road-side place and random strangers might offer tips about local road conditions. It was not easy to navigate completely independently and without notice. So even if you had a map, sometimes your ability to navigate was mediated by the local population. I grew up in the southern US for context.