Cars scale, because if on one day for some reason only a single person wants to go anywhere, only a single car will be deployed. And on the next day, when suddenly a million people want to go anywhere, up to a million cars will be deployed.
Getting stuck in jams is down to badly designed roads. For example the use of traffic lights, whose only job it is to stop the flow of traffic.
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If you need to take a bike or walk, then why not just go to your destination that way? I'll also have you know that not every passenger can have a bike when riding a bus or train. Capacity doesn't allow for this.
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What use is a rental car for carrying lots of stuff? First you need to go to where the rental car is and then you have to bring it back. Unless the rental car can drive by itself to where you are and drive by itself back it seem really cumbersome.
The issue with carrying stuff is that this will come up eventually and once you already own a car since you have to, why not use it when you don't necessarily have to, just because it is convenient?
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Can't do much about society. We unfortunately do not lock up insane people anymore and there are even talks of putting mentally disabled people into normal public schools. We live in crazy times.
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You WILL definitely wait up to 2h, maybe even longer. In fact, you will just be happy that eventually something does show up to take you home. Of course, you can then declare that whatever system you have is not a "decent" transportation system, but it will be reality, unless you live in a state capital and only travel within the city. Once you need to travel to a different state all bets are off.
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My argument isn't that that cars are better and more convenient than public transport, my argument is that public transport has inherent issues that are impossible to solve and can therefore never replace the role cars have in society as the default.
I hope for a future with cars on demand, where they drive to your home by themselves, you use them, and then they drive off by themselves. But even that won't work very well as it means other people using these cars and thus their cleanliness being in jeopardy. Guess the only way to solve that is by using something I don't want: a surveillance state.