I've been going around the maps and I've found that there's debris or roadblocks were the road would continue outwards. Now I know this stuff is for us to not drive on to very low quality roads and Terribly rendered terrain. But I would like to know if you know of any maps that are made up of a single LONG road,.
There is also this: https://www.beamng.com/resources/american-road.3100/ There are a few large maps getting around. You of course sacrifice quality for the size. Mainly in them being more sparsely populated. They also tend to be difficult to run.
There's this one too. A bit outdated, but works fairly well on low-end computers. https://www.beamng.com/resources/desert-highway.50/
Oh, I forgot this one. It's really good for cruising, I could drive over 400 km/h without crash on this map: https://www.beamng.com/resources/las-colinilas-de-vapor.18460/
Los Injurus is my favorite big map. It's not one long road, but many. To give you an idea of the size, the airport alone is bigger than a lot of maps, and it's a tiny corner of Los Injurus. The runways are so long, you'll max out, overheat, and get bored with most drag configs before you reach the other end.
If you like from oldschool retro content, then this conversion of old rFactor1 map might work for you: https://www.beamng.com/threads/cannonball-run-usa-huge-fast-roads-map-update-2-more-traffic.80011/