The tunnel diameter is much smaller. Like 1890s-built London Underground diameter tunnels.
The standard with US subway construction today is massive tunnels with huge, expensive stations. Seems to be a design choice from Musk.
The standard with US subway construction today is massive tunnels with huge, expensive stations. Seems to be a design choice from Musk.
That said, I don't have any particular insight into the field itself; however I do have a respect for Musk's ability to rephrase the problem just slightly (e.g. landing boosters to save costs) and to turn the whole economics of the situation on its head.
How? These pods take 16 people, and per the article, only one can set off every 30 seconds. This limits capacity to 2k people per hour (even assuming that it manages the promised numbers, and historically Musk stuff doesn't), which is far less than one would expect of a decent bus rapid transport line, never mind an underground train.
Parallelzation applied to subways.
Single big trains get delayed due to any number of reasons - something on the tracks, broke-down train, etc...
With 10 smaller tunnels, they can just be rerouted.
Generally, every city has big transportation hubs - airports, train stations and so on - located at strategic places within the city. Musk's idea is to ditch these hubs and replace them with more frequent and much smaller stations which get you closer to your destination. On the other side if they don't have to move millions of people to the same hub but rather move a much smaller number of people, they can afford to dig smaller tunnels and stations which are way more easy and fast to build.
For instance, in London every time they build a new transportation hub, it takes years. These stations are massive, they literally dig in every direction for several meters.
I don't know if it's going to work but surely there's thinking behind it.
Edit: typo
This also could really only be the long time play anyways - it's the only reason using autonomous battery powered model X's as the "cars" makes much sense.
I think it's an interesting idea, Musk obviously likes his sci-fi. He is basically attempting to implement packet switching for human mass transport vs. the current circuit switching we have.
The actual cost of tunneling itself is generally fairly cheap--somewhere around $50 million / mile. The expensive part is the stations. You can probably save money without having to build mezzanines, but the lower utilization of the tunnel and the greater number of vertical access shafts needed (not to mention the challenges inherent in moving through that very crowded portion of real estate) is probably going to cause cost blowouts compared to subways. Particularly if you design the tunnels to move cars, not people (SOV cars being about the worst use of space possible).
Building a new network would not be constrained by existing implementations. For example, you can't just drive the trains faster on existing systems. Everything would have to be redesigned/upgraded to do it - the motors, tracks, track bed, brakes, suspension, safety equipment, schedules, signals, everything.
That doesn't answer the question. Why would the transport be "correspondingly faster" in a smaller tunnel than a bigger one, given both are new digs?
If the units/hour capacity can be met with a smaller tunnel running fast little pods on a single track, then boring out a larger tunnel that could fit perhaps three tracks would be redundant.
And that assumes that the pods could run on adjacent open tracks like railcars, whereas the intended design may require a smaller tunnel bore that is close to the size of each pod.
If you have 4x as many trains but don't load and unload on the same platform you could easily get by with 1/4th as many passengers per train.
The factors that limit train frequency are station dwell times and switching time. A subway line can generally hit 26TPH, and the top speed of most subways is usually about 70mph, with average speeds generally being in the realm of 30mph. Making trains faster actually reduces capacity; a HSR that goes 220mph is considered to have a capacity of around 4-6TPH. You can also improve throughput by cutting out all branching; Moscow gets about 40TPH as a result, which is about the feasible limit of rail systems.
30 MPH which is low = 5280 * 30 = 158,400 feet per hour / 26 TPH = 6092 feet per train. Actual subway trains are 600 feet or less long ~= 10% utilization. At 30MPH cars don't keep 126 feet between each other. Bump that to 60MPH and the trains are at 5% or less utilization and again cars don't keep 266 feet between each other even if they should. And again this is very long 600 feet subway trains most are significantly shorter than that.
Further trains have a stopping distance @ 62MPH of 820 ft with (0.15 g) deceleration. High speed trains can get an extra 0.3 m/s2 deceleration which could also be added to normal subway trains but would be an emergency situation as they knock people over.
PS: At 60MPH the theoretical limit is over 220 trains per hour assuming all trains can stop before hitting the train in front of them. But you can only approach that with full automation and multiple lines for acceleration.
We can also exclude any car stopped at a station, as you can have multiple cars unloading at the same station or have a train bypass a station without making a wider tunnel.
Sure, but we're talking about subway networks underneath major metropolises, and adding extra tunnels and platforms is basically as expensive as digging a whole new line - when it is even possible due to space or geological constraints.