It's not about being bigger, but having high population density.

Obviously in larger cities it will take longer to travel from one extreme to the other, but that is a similar problem as trying to travel to another city. Trips that are 20km long need to be treated as such, no matter if they're in the same city or not.

Some suburbs in Barcelona and Madrid have more than 20K hab/km2. And they are expected to have as low car transit as other European cities with around 3K to 6K hab/km2.

It is obvious that even though lots of people might be able to switch to alternative ways of transportation car is still extremely useful for many use cases.

The solution is the right city design: more populated areas in the district centers, and less densely populated areas towards the outskirts. Spain is terrible at this, as they design high density areas everywhere. Americans do the opposite, it's mostly all low density.

A balanced solution is how dutch cities are designed. You can live in your own garden house, while having access to commerce, offices in higher density areas, just by 5-20minutes by bike (up to 5-6km).