Canada

Yeah, the total direct monetary cost of maintaining low-density car-dependant cities is extremely high: road construction & maintenance, plumbing and electrical, parking lots taking valuable space that could be used for housing or workplaces, insurance for personal and commercial vehicles, maintenance and upkeep, gas, and probably many more I've missed.

And on top of all of that, the externalized monetary costs are also high: medical costs from all the deaths or injuries due to collisions (the stats are honestly depressing), medical costs due to less physical activity across the population, environmental damage, time wasted due to traffic, slower delivery times for long-haul trucks, and probably many more I've missed.

And on top of all of THAT the intangible costs are also high: isolation from the people and communities directly around you, less customers for small businesses that rely on foot traffic and have no parking space, increasing polarization between urban/suburban/rural populations, and probably many more I've missed.

Side note for the people that still really need cars in their lives (workers in rural areas, people living in suburbs, etc.), pushing for better transit and city planning will directly benefit you. If less people have cars: gas prices will be lower (supply and demand), road construction and upkeep will be cheaper, traffic will be better for you directly, and more. I always fear that pro-transit, pro-urban planning folks (me included) come off as dismissive. There are definitely people who will still need cars in their lives. The goal is to catch the many millions of people who could probably replace their car usage if transit systems and cities were built better.

People will always do what is easiest/best for them, we need to keep pushing towards systems that make sense.