Maybe it’s because my course of study in my earlier life was engineering (I planned on either mechanical or civil engineering, and wound up in media. Short, but happy story. Maybe over a beer sometime.) But I confess being intrigued by the idea of all these underground tunnels, even though - like the Mayor of Las Vegas who recently voted “yes” on the expansion - I have serious doubts about the viability of the whole thing.
Here’s a story, which includes a map of the many and various (for now theoretical) stops for the system, more than 90 when all is said and done (the recent city council vote authorizes a look-see at adding 21).
I note that they are not all in a straight line, and the question upthread about having sidings for loading and unloading got me thinking about the Boring tunnels. For instance, when you have a siding, or a branch, you can’t use one of those tunnels, because it’s hard to turn left when there’s a concrete ring in the way. But you need the ring for stability from the ground pressure so the whole thing doesn’t collapse.
This has been overcome in a variety of ways, of course, even with old school tunneling, else the subways of New York couldn’t exist. And in fact at least one of the Boring tunnels have done this in Las Vegas, using the old-school “cut and cover” method, rather than switching to a “twice the size” boring head so two lines could merge/diverge.
Sidebar: It seems to me an elliptical tunnel would have many of the same advantages: an arch support overhead, a flattened bottom, and wider space in between. And you can turn a circle into an ellipse just by angling it 30° or so, so if they chose to build a tunnel borer with a 30° angled head it would produce an ellipse rather than a flat plane circle. I’m sure they’ve thought of this, although I’ve never heard of it being employed anywhere. Sidebar off.
If you look at the map in the link above you will notice that all the eventual stations are not lined up in a nice straight line, like say a route from the airport to a hotel, or to the convention center might be. That argues not only for stations, but lots and lots of branches and turns, which means merges and splits of real time traffic and cars. (Not insurmountable by any stretch, just get the cars to talk to each other and merge, although they’re talking about having them run with only a few feet of separation in many cases, so that might be dicey.)
But now think about coming in from the airport and turning right. Simple, just branch off to the right. OK, suppose you need to turn left? Not so simple, assuming there’s another tunnel going back to the airport in the way. How do you do that? On the surface you do a stop light, or a ramp/flyover, or maybe even a cloverleaf if it’s a busy interchange. You could do all of those things underground, but your cost of tunneling is going to skyrocket - or you’re going to put stoplights in the way, or you’re going to risk collisions if you hope software allows direct crossing. (Anyone who has played with a model train setup with a 90° crossing knows what I’m talking about.)
So again, not insurmountable, just not as easy as “bore a hole” simple. You could ease this somewhat by having the two airport tunnels at different levels so a left turn would go under (or over) the one in the way, but then your ramps in and out are going to be longer, and there are still going to be times when the opposing tunnel is just in the wrong place. Darn it! And you’re going to be popping up and down if you want to cut costs by using the same level stations, so…
The comments of the reluctant Mayor of Las Vegas in the link above are interesting. Some are simple to dismiss, others not so much. I do hope that some of the planning for this involves a holistic approach. (For instance: A better subway for New York would have been one that stops every 4 blocks, regardless of what was above, rather than trying to hit the major points and leaving some places a 10 block walk from an entrance. In that way the maximum walk for anyone would have been 2 blocks, which would help the city spread more evenly and not leave “transit deserts”.)
As BT noted above, there is a multifaceted approach being taken, with multiple options for travel - and that’s good. I would guess the tunnel is the most expensive, and offers the least capacity of all of them, but then it’s Las Vegas: lots of touristy dollars not so concerned with “value” as “fun”, and it might work well for them. That whole city has been built on outlandish ideas, this could be the next.
Or not.