> No more hierarchical/dendritic street layouts.
It's worth playing some Cities:Skylines (which has a fairly accurate traffic simulator, particularly with the Traffic++ mod) to understand how the road hierarchy came into being. Or, for that matter, trying to drive through a grid-based city like Manhattan or SF.
You get very large traffic jams. The problem is intersections, and particularly intersections where traffic backs up to the previous intersection. When this happens, a traffic jam tends to spread across the whole city; incoming traffic can't clear the bottleneck fast enough, so the bottleneck just grows like a cancer until it envelopes a whole neighborhood.
Oftentimes, the solution to a traffic problem is simply to bulldoze a few intersections. By doing this, you give cars a buffer. It increases the median trip length but it also increases vehicle speed and road throughput by more. It turns out that the major contributor to traffic jams is the acceleration of having to start/stop at traffic lights and when turning.
Self-driving cars (or just ubiquitous turn-by-turn navigation) could change this equation by intelligently routing cars around bottlenecks and avoiding the neighborhood entirely, but as long as drivers have imperfect information about traffic conditions and tend to take the shortest route to their destination, this will remain a problem.
(I've had great success with using pedestrian paths to provide cut-throughs between dead-ends and nearby intersections, though. And with providing pedestrian paths under or over those intersections so that people don't have to wait for stoplights to cross the street and don't stop traffic with their jaywalking. The game unfortunately has pretty terrible pathfinding for pedestrians and won't let you build compact staircases, so this limits their usefulness to real problem intersections, but in real life I think many suburban cities could drastically improve their walkability/bikeability just by building raised pedestrian footbridges over their major arterials.)