This is similar to how my bases are constructed, but since I play on a server with other people, I dismantle the sections in-between bases so that’ I’m not cluttering up the map. Remember, even if they aren’t physically connected anymore, because they were built on the same snap-grid, they will continue to share the same decay timer.
So you might consider making a backup of your game, deleting the intermediate roadways, and seeing if that helps. For doing the deletion, you’ll probably need to make use of admin mode to do radius deletes unless you are immune to boredom and/or repetitive strain injuries.
In case you need it, the path to the save files should be here:
C:\Program Files (x86)\Steam\steamapps\common\Conan Exiles\ConanSandbox\Saved
Just make a copy of game.db and name it something obvious like gameWithRoadways.db or some such. If you don’t notice any change with the roads deleted, you can then erase the game.db with them deleted, and rename the backup copy to game.db again.