Okay, that is the proposal I've seen, and IMO it has a huge number of flaws.
- There are going to be certain places where you can't dig a tunnel for geological reasons. For example, half the population of Florida lives less than 4 feet above sea level.
- Even if you increase the speed you can dig a tunnel and lower the cost, it's still cheaper to pave a road above ground.
- There are plenty of places where NIMBY folks just wont let you dig a tunnel (looking at you LA purple line extension).
Ignoring all that though, even if you can build an entry point every half mile, you still run into the issue of needing to drive the car that last stretch, which means you need to either solve the problem of self-driving on complicated roads, or force the driver to take over. The tunnel system shortens the amount of time you would spend on small roads, but it doesn't eliminate it.
- There are going to be certain places where you can't dig a tunnel for geological reasons. For example, half the population of Florida lives less than 4 feet above sea level.
- Even if you increase the speed you can dig a tunnel and lower the cost, it's still cheaper to pave a road above ground.
- There are plenty of places where NIMBY folks just wont let you dig a tunnel (looking at you LA purple line extension).
Ignoring all that though, even if you can build an entry point every half mile, you still run into the issue of needing to drive the car that last stretch, which means you need to either solve the problem of self-driving on complicated roads, or force the driver to take over. The tunnel system shortens the amount of time you would spend on small roads, but it doesn't eliminate it.