Now I am wondering if it's customary for Roadgeeks to fail to include enough public transit in their cities. A dense enough city necessarily cannot rely on only automobile transport- it's a functional requirement, not a cosmetic choice. It's relatively uncommon for American cities to reach a density where transit is a necessity, however.
Cities Skylines, in particular, makes cities that rely only on road transport fairly difficult when looking just at the stock game. "Stock" vehicle mechanics are woefully under-coded, and you can get genuine gridlock really quick. Public transport makes this a lot less likely to happen.
In the case of the map above (that I shared), the vast majority of tourists, and a good portion of new residents, arrive to my city via the high speed rail system I have. The main hub is where the black and white line passes directly through that built-up area. At that station, there are several bus routes that connect the main city with the other suburbs. This definitely helps with traffic, especially if you're like me and use "no despawn" for vehicles (vehicles normally disappear into the drivers' pockets).
That is true. Things like cims deciding on their exact route, including lane changes, at the start of their journey, traffic and anything else be damned, really gunks things up. I remember once trying to separate the directions of an interchange (
like this) to stop the ramp from backing up onto the mainline, but no cims used the new ramp that was supposed to end the left turn movements because it was only faster when there was traffic (which there always was) and they don't take traffic into account. Add to that the inability to define turn restrictions without mods, and I ultimately had to ban non-local traffic from one side of the street (which worked because I figured out that the trucks were using the avenue instead of the freeway to get to an industrial area).
Traffic congestion also has more severe effects in Cities: Skylines than SimCity 4 because everything is agent-based... including city services. In SimCity, the worst that could happen is that homes start abandoning due to long commutes, and that took a while. In Cities: Skylines traffic congestion can quickly cause most city services to break down and stop functioning.
All this discussion makes me wish I was still able to pay the game. Unfortunately, while my computer was more than adequate when I first started playing, between needing more resources with each DLC whether you buy them or not and the Paradox launcher, the game is now unplayable on my computer (and I don't like the privacy problems of the launcher, either). I can't even go back to SimCity 4 since I can't figure out how to get it installed on my computer; Wine on Linux doesn't work well for things that need more than one disk to install, and SC4 is especially troublesome for some reason. None of the workarounds I have tried (which worked great for Civilization IV) have worked.