Here's a city I started on Sunday while I was hiding in my bunker from the riots celebrating some team winning some football game somewhere. In this city, I attempted to build it entirely without roads, which worked well for quite a while, until I expanded to the other side of the river. At that point, everything started to go south. I experimented by placing some roads on the troublesome side of the river, and traffic immediately exploded (from 9 to 70). So, I tried various things such as improving the mixing of zones to improve the situation for a while, and then got bored with that and burned down that side of the river, leaving what was left as a ghost town.