Have some people here not ever been involved in doing something for the first time? Something somewhat complex. Generally one starts with some assumptions and refines their ideas as things are tried and better ideas developed. We didn't get to the Moon by simply building a rocket and going there. We worked our way there through numerous steps, developing the hardware needed over time.
A few years back Musk proposed the hyperloop, traveling through an almost vacuum in a tube at speeds faster than passenger jets. He envisioned using an air compressor on the front of the passenger/freight pod to compress what air was in the tube and then blow it out through jets to position the pod equal distance from the tube walls.
There are a few problems with an above ground metal tube. Acquiring right of way can be difficult and expensive, lots of NIMBY sorts of issues. A metal tube exposed to sunlight is going to expand and then shrink as it cools. Which means a bunch of tricky expansion joints. And JoeBilly could easily shoot some holes in it 'just for fun', or more sinister people could blow up a section.
A solution to those three problems might be to go underground. In order to make a tunnel water tight it has to be more than capable of maintaining a partial vacuum. Tunnels are out of sight, out of mind. And it's not hard to detect someone or something digging its way toward the tunnel long before damage could be inflicted.
But there's the cost of tunneling. Musk and his crew of merry thinkers went to work and decided that by simply making the tunnels small they became much cheaper per mile. Then they worked through a number of thing that they could do to drastically lower the cost of tunneling. Things like almost constantly drilling rather than, on average, ten minutes out of each hour. Improving the cooling system for the cutter so that it could run at higher speeds. Finding a way to dispose of the wastes at no cost or even a bit of a profit.
Then bootstrapping. Building a hyperloop from LA to NYC would require a lot more than pocket change. The best route is probably building some somewhat short but very fast subway systems in which all rides are 'express', no stops between getting on and arriving at destination. Build some systems, sell rides, make profits, use profits to build a modest length hyperloop.
The cheapest initial vehicle would be to take an existing battery powered car that could safely travel at 150+ MPH in the tunnel and simply use it. Later a higher capacity passenger could be built but not until the first system is up, running, and making money. In fact, it would be very possible to take the Tesla S/X skateboard and bolt a eight or twelve passenger pod on in place of the sedan/SUV body.
Boring has demonstrated that they can drill a tunnel rapidly and at a very attractive cost. And that is using only a modified used tunneling machine. Boring has the next two generations of their custom designed tunneling machines in production.
Boring has demonstrated that they can use an 'off the shelf' Tesla and safely drive their short test tunnel at speeds in excess of 125 MPH. The first used 'guiding wheels' to keep the car centered in the tunnel but later showed that Tesla's lane keeping software could accurately steer the car. Yes, the ride was a bit bumpy but, remember, right up front Musk explained that the tunnel driving surface had not been installed.
Boring has demonstrated a prefab elevator that can be quickly installed and moves vehicles from street level to tunnel level rapidly.
Communication between vehicles and between vehicles and 'central command'? How hard can that be. Send out position and speed data a few times per second. If a problem develops issue an "All Stop" to all vehicles behind the vehicle with a problem. Sensors along the tunnel can serve to backup and verify data from individual cars.
Why would we want this to work? Imagine leaving your house in a robotaxi, riding a short distance to a Loop spur, changing vehicles, and then going to the airport 20 miles away non-stop at over 150 MPH. For small money. Using renewable energy.
Think about not spending a half hour or more each day commuting in bumper to bumper traffic but zipping to work and then back home, giving you an extra hour each day to do something other than commute.
Will it work? Maybe. Looks good so far other than finding places to build the first few projects that will be needed for proof of concept. (Or more proof of concept.) Boring can bore economically, run cars at high speeds, and move them from surface street to tunnel quickly. Now the remaining question becomes how inexpensive can they make it.