There are trains that transport cars.

True, they also run such a trains here in Finland, an overnight trip from south to north (Lapland). The train tickets for our family of 5 plus a car are so expensive (total 1200 eur) compared to minimal marginal cost for using our EV (150 eur), that we always choose the car.

highways don't go door to door, and that's what they were suggesting.

They were suggesting they want to use the same vehicle door to door with it being automated during the freeway bit. A train would still mean find some transport to the station, wait for the train, ride train, find transport from station.

Or a train that takes cars, like a Ferry, obviously that massively cuts down on space efficiency but it’s not impossible.

Called a Motorail: https://en.wikipedia.org/wiki/Motorail

Like the euro tunnel