Compare the above to hop in my car, drive to the freeway, turn on self-driving, turn off self-driving once i get off the freeway, find parking near where i'm going and walk in.
As a society, we've done alot more in the name of convenience.
And you need a fleet of rental cars so that people can actually get to their destination.
What's the relative cost of all that vs. pavement?
Commuter rail systems run at 2 minute headways or less. Long-distance trains mostly don't but that's largely due to excessive safety standards - for some reason we regulate trains to a much higher safety standard than cars. Even then, the higher top speeds of trains can make up for a certain amount of waiting and indirect routing. (Where I live, in London, trains are already faster than cars in the rush hour).
> What's the relative cost of all that vs. pavement?
When you include the land use and pollution? Cars can be cheaper for intercity distances when there's a lot of similarly-sized settlements, but within a city they waste too much space. And once you build cities for people rather than cars, cars lose a lot of their attraction for city-to-city travel as well, since you're in the same situation of having to change modes to get to your final destination.
That "some reason" is physics. According to a quick Google search, an average race car needs 400m of track length from 300 km/h to 0 km/h. A train will require something around 2500m, over 5x the distance, to brake from the same speed. Trains top out at -1.1m/s² deceleration, an ordinary car can get -10m/s² deceleration.
Part of the reason why is also that in a car, people are generally using their seatbelts - which means you can safely hit the brakes with full power. In a train, however, people will be walking around, standing, taking a dump on the loo - and no one will be using a belt. Unless you want to send people literally flying through the carriages, you can't go very much over that 1 m/s² barrier.
Because of this, you have the requirement of signalling blocks spaced in a way that a train at full speed can still come to a full stop before the next block signal. Also: a train can carry thousands of people. Have one train derail and crash into e.g. a bridge or crash with another train and you're looking with way, way, way more injuries and dead people than even a megacity could support, much less in a rural area.
If the cars are electric, I'm less sure.
Though your train of cars would likely have such low passenger density that a series of buses would be just as good. Special lanes just for buses are already a thing.