No cars on the roads works for short periods of time, but with 15 million people living in e.g. the London metro, you need something to move 15 million people's worth of living logistics (food, goods for sale, garbage removal, etc.). Those are all carried by wheeled vehicles, whether it be cars, vans, or lorries. The niceties of the suburban or urban areas aren't possible without them.
Even if they were all electric or powered by unicorn farts or whatever, it's still millions of multi-ton steel vehicles zipping around leaving as much trace as a multi-ton moving thing would. I grant you at least the air quality would be better without internal combustion.
In the end, all Europe is filled with cute little walkable towns, yet people still congregate to the congested, filthy, car-filled metros, for some reason. And at a certain level of built-up population density, you just can't have a very nice natural environment; the brief moments of peace you observed during the Covid lockdowns or whatever can't last, because that would mean the city itself dies.
It's also dishonest to not include an answer for personal transportation. "Public transit" is a handwavy answer, since obviously if personal transportation means are removed, more public transit will be needed, meaning more vehicles (be it trains, buses, or taxis) will be on the road.
Unless your solution is that people should just move less?
To be fair, if people just stayed in their houses and didn't use electricity or water and stopped eating and just died when they ran out of food then we could have the whole CO2 problem wrapped up for a good 1,000 years or so in about 40-60 days, assuming they also took the time to gracefully shut down any operating machinery and safely disposed of any hazardous chemicals while waiting for their impending death.
Humanity might go extinct in the process, but they would have at least stopped further destroying the only planet they have to live on in the process.
Even if they were all electric or powered by unicorn farts or whatever, it's still millions of multi-ton steel vehicles zipping around leaving as much trace as a multi-ton moving thing would. I grant you at least the air quality would be better without internal combustion.
In the end, all Europe is filled with cute little walkable towns, yet people still congregate to the congested, filthy, car-filled metros, for some reason. And at a certain level of built-up population density, you just can't have a very nice natural environment; the brief moments of peace you observed during the Covid lockdowns or whatever can't last, because that would mean the city itself dies.