This guy made 400k population city without public transportation with L-based streets -
http://www.youtube.com/watch?v=qV6PrEjaH8Q&list=LLLvq9KX4OlKxx5vA-DX3UqQ
Yeah, traffic behavior needs fixing, because its stupid, but You can counter it with Your city design even now.
I looked at it, and it looks based off of a false mathematical assumption (an L road connecting back to an avenue is always equally long as the avenue) and a lack of understanding the shortest path-find algorithm. I can't get his city to be working as it does outside of anything besides sheer luck. He's mixing commercial zones with residential, which helps on commuter traffic, but not at all on delivery-truck traffic. Maybe that's OK, since there are more commuters than trucks, but I haven't figured that out yet.
I thought I had figured out how the path-finding algorithm chose between two roads that are equally long - that if it comes to an intersection and finds two of the ways to be equal total distance, it then chooses the one with the longest, uninterrupted road. This seemed consistent for a while, but then my city layout didn't yield the results I wanted. So there's probably a last detail I'm overlooking (like an affinity to continue straight instead of turning).
There are three changes that needs to happen:
1) Weigh the road based on road type. The more I think about it, the harder it seems to do, because it seems the entire game is based on an "agent" not being discriminated against for being a car or an electricity agent. That's annoying. But maybe it still would've worked. Anyway, you report back that a dirt-road is twice the distance (or more, based on testing) as an avenue, and increment the "weight" (or reported length) based on road-type. That way, cars would automatically choose the assumed FASTEST way to get somewhere, not the shortest way.
2) Agents have sinks (a delivery truck delivers goods. A car delivers a sim home - that's a sink), but when they set out to go to their sink, they don't claim the sink they're going for on their outset. This makes it to a race to get to a house first, for all sims, and it looks like a game of musical chairs, and it looks ridiculous.
3) The absolute bonus (and sadly, the only one Maxis is working on, it seems) - load-balancing based on congestion. It will work, but it's kind of silly that 30% will take an adjacent avenue while 70% stand staggering down a street, based still on the completely flawed algorithm of choosing two equally long roads. ALWAYS PICK THE ONE CONSISTING OF AN AVENUE. Gah.
At least that would make us square-city builders incredibly happy.
Eh, it's comprehensible. I once read an article on Gears 2 that stated the issue succintly - they spent 40,000 hours testing the game, which seems like a lot, but gamers put more time in the first hour after release.
The game needed a real, actual, beta test, where people would try out all sorts of things that the developers didn't even think of. I would say that it is incomprehensible that they didn't do that beta test, sure.
It's such a basic problem that ANYONE that tries to build a city runs into, so, it's not an obscure bug, what so ever.