The problem with Simcity is that 'traffic' would basically take absolutely any turn that would get them to where they wanted to go. This meant that if you had a gridded layout of large, wide avenues, four-lane primary streets, and two-lane side streets, your traffic will gladly back up for miles outside of town because everyone entering your city is trying to take a two-lane side street to get to their destination, even if it's on an avenue, just because turning onto that side street is the first available option.

They later updated the algorithm, apparently, to do path cost routing, making it far more preferable to take avenues over dirt roads, but until then the only way your city could work at all was to create it entirely out of cul-de-sacs.

There was also an issue with the train service, where, when a commuter train came to an intersection, it would randomly choose which direction to take. This meant that if you had a grid of avenues, some of your sims would be waiting for hours for a train, because the train is bouncing randomly around your downtown instead of dropping anyone off.

Moving to a system where there were literally no intersections at all for your trains was the only way to make your mass transit system a benefit and not a liability.