191–200 of 237 posts
Is digging down really cheaper than going up? Chicago has got an elevated train [0] and even double decker streets [1] and those don't have lots of the problems that tunnels do like ventilation, escape tunnels, and moving all the dirt. [0]: https://en.wikipedia.org/wiki/Chicago_%22L%22 [1]: https://en.wikipedia.org/wiki/Wacker_Drive
Twitter thread on the physics to go 150mph in this tunnel: https://twitter.com/Model_4_/status/1075270290978963458?s=19 Note that air resistance is a much bigger problem in a cheap, narrow tunnel.
I imagine it’ll also probably be hell on tires. You’d need W- or Z-rated tires to do that and those are $$. Perhaps smooth concrete will mean lower rolling friction along with lack of sudden maneouvers. Still, going that fast is expensive in all sorts of ways.
High speed automotive tires are expensive because they need to withstand all the flexing that comes from running at high speed with the kind of inflation pressures that deliver what the owners of the high dollar cars they go on consider a reasonable ride. They have to be fairly soft/flexible tires for the same reason. A hard, stiff tire would not deliver the kind of traction people expect from a German driving machine.
Basically you have speed, weight capacity and ride quality and you only get to pick two. So long as you can compromise somewhere everything is easy and cheap. A boring old light truck tire will live a long life at 150mph so long as you run it at a very high pressure and light load.
If you want to see this principal in action look at small trailer tires (like snowmobile and jet ski trailers). They carry a ton of weight (for their size) and run at very high speeds (a sub 20" tire is really spinning fast at highway speed) by running very high pressure with a stiff sidewall and the kind of rubber that makes butter look like a high friction surface.
So yeah, tires are the least of their technical issues.
Earlier quoted context omitted.
You're comparing a prototype with a real life operating system that was built to be um, you know safe and good, unlike what has been shown with this prototype. The fact is that a 500 capacity train running at 75-100s headways destroys this system capacitywise. Musk has a long, long way to go before he shows that this idea of his is better than the 1986 era technology at the core of Vancouver's system.
> The fact is that a 500 capacity train running at 75-100s headways destroys this system capacitywise. This is like that linked tweet: all assertion, no data. What are you using to estimate the theoretical throughput of a Boring Co tunnel system vs Skytrain? Let's debate that. Right now it's all just thin air. Assumptions I'm willing to believe, and thus make me interested in this prototype's viability: 1. Cars need…
Basic geometry.
Earlier quoted context omitted.
But 75 cars spaced 1 second apart...
Somehow you assume they will be able to get into that tunnel at these intervals
This plan is like when a city widens a highway but doesn't touch other parts of the road network? What happens? It just moves the choke point somewhere else in the network.
Earlier quoted context omitted.
I imagine it’ll also probably be hell on tires. You’d need W- or Z-rated tires to do that and those are $$. Perhaps smooth concrete will mean lower rolling friction along with lack of sudden maneouvers. Still, going that fast is expensive in all sorts of ways.
People go 250 kmh on German highways regularly (unfortunately). It doesn't seem to be unpractical.
Earlier quoted context omitted.
> The fact is that a 500 capacity train running at 75-100s headways destroys this system capacitywise. This is like that linked tweet: all assertion, no data. What are you using to estimate the theoretical throughput of a Boring Co tunnel system vs Skytrain? Let's debate that. Right now it's all just thin air. Assumptions I'm willing to believe, and thus make me interested in this prototype's viability: 1. Cars need…
> What are you using to estimate the theoretical throughput of a Boring Co tunnel system vs Skytrain? Let's debate that. Basic geometry.
Earlier quoted context omitted.
The problem with subway systems is that they are great once they have enough reach and stops to reliably and frequently get you were you need to go without needing a car. However, a small subway system with infrequent service and only a few stops isn't all that useful. If we take the claims here at face value (not saying we should) then this is a solution that provides value immediately for people commuting by car, a…
Uber buying a major cities metro system and making it not shitty would be pretty great. NYC subway is basically what taxis used to be, dirty and hostile toward the user.
> "Still, the $10 million is orders of magnitude lower than a typical subway project, Musk said." Umm, and the capacity of these tunnels is also orders of magnitude lower than a subway. It would also be a lot harder to use and available to far fewer people. This entire idea should be laughed out of existence, but despite everything, Musk still gets fawning coverage for any crazy idea he spouts. Maintenance will be im…
Even assuming that capacity/dollar is actually worse than subways, they can still be economically superior, for the same reason solar+battery is beating nuclear. The ability to incrementally build capacity relatively quickly and with relatively low, incremental costs beats any system that requires billions of initial investment and only comes online in the timescale of decades.
And I really don't think that capacity/dollar will be worse than subways, assuming that he intends to build off-ramps for leaving the system, as alluded to in the stream. Simply removing the need to stop at every exit greatly improves capacity, and while the capacity of an individual tunnel is still much worse than a single subway tunnel, they can just build more.
> Maintenance will be impossible. Breakdowns of any sort would go from being annoyances to a few to being catastrophic failures for the system. Even if the tunnels never degraded, even if no car ever had a flat tire in the middle of the tunnel, and even if you could actually achieve 150mph (which would be extremely unpleasant for the passengers anyway), you couldn't physically fit enough cars through the tunnel to compare to real transit system.
You seem to be assuming a single tunnel per direction. Assume 20 instead. Suddenly a car failing in the tunnel turns from a catastrophic failure into one that causes some traffic to have to take a little extra time as they back their way to the closest cross-tunnel, and a relatively minor loss of capacity until a recovery vehicle can come pull the broken one out.
And as Musk said like a dozen times in the stream, he intends to match a real transit system not by increasing capacity per tunnel, but by starting building tunnels and then not stopping until there are no more traffic issues. Since he gets to expand in three dimensions, he can just stack them on top of each other.
> Given that this thing requires rigging something up to your vehicle, the onload and offload points would immediately become major bottlenecks to any serious throughput even if you could cram them in bumper to bumper.
Their demo had the "subway wheels" deploy automatically, while in the elevator. For high-throughput exits, they probably need to bite the bullet and just build off-ramps.