It would appear there becomes a point where regardless of how few resident zones are on a road they demand road upgrades. I'm beginning to think trying to avoid upgrading roads is futile. But what I'm wondering is will upgraded roads reduce traffic on connecting not upgraded roads? This assuming that traffic flows from A to B and isn't strictly a population count vs length of road between lights. Though I suspect it is probably nothing more than that metric rather than an A to B thing. But I figure I'd post here to see if any more info has come about since the starting of the thread that will be helpful.