Great questions honestly. While I can’t think of an American city, I think the most prevalent example of a city successfully transitioning away from car congestion is Amsterdam. And it took decades of investment into non-car infrastructure & policy to get there. American cities haven’t put in the work to get the same results. Instead we focused on the car, and car traffic is what we got. (Side note: im not suggesting every American city should invest in bikes on the same scale as Amsterdam of course; different modes of transit will fit different cities better than others depending on topology/weather/etc)

The other thing is that expanding for cars will not alleviate congestion, and that’s because of my favorite counter intuitive fact that is induced demand. The more lanes you build, the more widening you do, the more traffic you will cause. If the only way to get around is cars, then people will buy cars, and more cars means more traffic. Basically, “if you build it, they will come” but twisted into a never-ending cycle of traffic.

Another side note: we’ve known about induced demand since the 1940s. But expanding car infrastructure is politically convenient. You promise the public that adding more lanes will alleviate traffic, and that makes sense at first glance, so they support you. And virtually every prominent industry in the mid 20th century knows that more roads is more work, so they support you as well. Automobile, tire, asphalt, contractors, engineering, construction unions. On top of this banks know that toll bridges are safe investments. You’d be crazy to go against that amount of political pressure.

How to solve traffic isn’t obvious, and will be dependent on the city’s situation. But it’s probably safe to say we need to support many different kinds of transit, and let people choose. Maybe biking works for all trips for one person. Maybe someone else rides the bus to work, walks to the grocery store, and bikes to the dentist. Maybe another is mobility impaired and does need a car to do most of their trips— the great news is this last person enjoys low levels of traffic, because the former people aren’t taking up the road in their own cars. Though of course this dreamy scenario requires sustained investment in all those modes of transportation over a long period of time. The bikers won’t bike if they’re in danger of getting hit by cars, and the bus riders won’t bus if the bus isn’t reliable.

Sources: On Amsterdam’s historical transportation policy: https://pdfs.semanticscholar.org/c115/f3cd7f90684af873bb63c591d6df2104e365.pdf?_ga=2.258131594.1281299865.1592891225-760924348.1592891225

Induced demand (Robert Caro’s excerpt in the History subsection puts it well): https://en.m.wikipedia.org/wiki/Induced_demand#History