Cities scale with busses and trains. For some reason, the boring company wants to scale a city with cars. You build this big expensive tunnel to get 1/10th or even 1/50th the throughput that you could get with a train system.
Maybe that's not the California way though.
If he had his way, he'd probably put rentable self-driving cars back-to-back in those tunnels. It'll be like aluminum and steel train cars, except each one is a Tesla.
You're missing that the boring premise is to utilize electric mass-transit units within the tunnels as well. That could dramatically scale the transit systems. It becomes a defacto variation of a subway system. Musk keeps pointing this out and it keeps getting ignored for some reason.
Consider that many folks don’t want to buy a car in some of these bigger metro areas or to pay for the parking to maintain one. For so many reasons, beyond technology, traditional mass transit is the superior option.
I couldn’t care less whether Musk achieves his technological goals with the Boring Company. It’s hawking an inferior product even if he does.
Elon has some good ideas and some stupid ideas, this is of the latter category.
The plan would to be able to pack cars at 100x the density of trains.
There's one catch for trains though: most trains aren't dispatching single cars. Rather, trains on busy systems are generally 8 or 10 cars that move as a consist. If you factor that in to your example, you don't have 120s between cars, but rather 12s. That might sound like a lot, but you should have 3s between cars for safe driving anyways, and train cars carry well over 4× the number of people in individual cars. Even if every road car were full Jitney vans.
This system is also nice because people could choose all types of different ways they would like to travel. From sleeper cars, to mobile offices, to cramped seats on a bus, to stand-only packed in like-sardines, we are now in a Japanese subway situation.
But as it runs on skates, do they want everybody to input their routes first? And clearly, it's going to cost so much now than surface highways, but economics is lost here, for people are convinced that a maglev train in a pneumatic tube will cost 6 billion, but a high speed rail will cost 80 billion. The name Elon musk is like magic to dispel any economic sense.
Conceivably, the utilization of the tunnel could be way higher than the utilization of train tracks (most of the time: empty)
You're not getting 150+ cars in that tunnel during the same time period.