I suppose if you regard sitting in a seat not being able to move as comfortable.
But before you get too relaxed in that glorious possible future:
1) high speed trains exist and proven - no new science or engineering to figure out
2) autonomous cars are constrained by the realities of space to put the vehicles. Too many vehicles, autonomous or otherwise = congestion and slow travel.
3) At 6 hours, this is nearly twice as long as the train will be.
4) In the autonomous car, you will need to stop for food and bathroom break. The train does not need to stop. So your trip time is extended, especially true with kids.
5) At 3.5 hours, someone can leave for LA at 6am - get to a 10am meeting and return in time for dinner and bed. Not going to happen if each direction takes 5-6 hours.
I really like high speed trains but have you paid for them? They are great for business where you need to go somewhere and come back, but for a family of 4 they are extremely expensive. From Tokyo to Osaka ~350 miles, it's about $130 per person each way on the Shinkansen. For 4 of us (2 adults, a child, and a free toddler), it would be ~$650 for round trip tickets.
But before you get too relaxed in that glorious possible future:
1) high speed trains exist and proven - no new science or engineering to figure out
2) autonomous cars are constrained by the realities of space to put the vehicles. Too many vehicles, autonomous or otherwise = congestion and slow travel.
3) At 6 hours, this is nearly twice as long as the train will be.
4) In the autonomous car, you will need to stop for food and bathroom break. The train does not need to stop. So your trip time is extended, especially true with kids.
5) At 3.5 hours, someone can leave for LA at 6am - get to a 10am meeting and return in time for dinner and bed. Not going to happen if each direction takes 5-6 hours.