How good are American roads?

Keeping roads perfect requires taking them out of commission for repair... which is a disaster on California freeways that have constant traffic. I think CA does a fair job of balancing that with road condition, and I assume they are already using more durable and expensive road construction methods than other areas that lacks so much constant heavy traffic.

I wonder if California would be better off with more Carmageddon type projects like when they shut down the 405 for like a week and hammered out necessary work.

If you shut down one freeway in the LA or SF area, every other one grinds to a halt also- including essentially all non-dead-end local roads... you might as well shut them all down at once, but there aren't enough road crews to repave them all in a week.

Above a certain population density there isn't really any way to use cars that isn't awful. When I was in Socal I would often meet people 10-20 miles away, e.g. for an after work bar trip and ride my bicycle - and beat all of the car drivers by a long wait.