The difference of car usage between USA and Europe should be much larger than the difference in car ownership. A car is useful for many things other than the daily commute, someone who mostly bikes to work is still rather likely to own a car but contribute much less to the traffic and pollution.

[edit] looking at random stats such as http://internationalcomparisons.org/environment/transportati... seems to confirm that - the vehicle ownership rates are just a bit lower, but annual distance driven per capita in European countries is twice less than USA.

This is probably a function of distances between living space and work. Beyond 10 km the car catches up and starts to get ahead in total travel time. Public transport is meant to close this gap but there's not enough for people, much less bicycles, especially long distance. So it gets crowded. The car is universal until you run out of parking space.

Do roads not get crowded where you live?

Here in Silicon Valley, there's no more room to widen 101.

Roads always get crowded; broadly speaking, making them wider increases the number of people willing to use them until they fill up again.

They do, but not enough to ensure longer distances are inefficient.

And especially the "ingress" roads do not block - from suburbs and further districts.

Now that is Poland, Warsaw, the city is designed to be more car friendly than most capitals in EU, more spread out, while still keeping strong public transport and bike as options.

The parts that block up are near choke points, City center, bridges, some big intersections.

We have a car. My wife and I still cycle to work each day.