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Elon Musk doesn't understand geometry

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Re: Elon Musk doesn't understand geometry

#21

Post by yongjik »

quantumwannabe wrote: post #20
caditinpiscinam wrote: post #16

Earlier quoted context omitted.

I don't understand your point about time; how does 20 small vehicles not take up more room than a bus?

The bus and the 20 AVs have the same throughput (40 passengers in 10 minutes). While the AVs take up more physical space than the bus, they require the same amount of road space to transport the same number of passengers in the same amount of time. You have to have extremely short bus headways before the road space efficiency tilts back towards its favor.

Seems like you're basically saying "It doesn't matter because the same road can support either a bus or 20 cars."

(1) This is a bad metric because it means everything is equivalent until traffic jam occurs. (Why stop at 20 cars? How about 2,000 cars?)

(2) More importantly, everything cannot be equivalent because traffic jams do occur in any respectably-sized city. Having 20 cars instead of one bus absolutely does contribute to having more frequent and severe traffic jams.

Re: Elon Musk doesn't understand geometry

#22

Post by quantumwannabe »

yongjik wrote: post #21
quantumwannabe wrote: post #20

Earlier quoted context omitted.

The bus and the 20 AVs have the same throughput (40 passengers in 10 minutes). While the AVs take up more physical space than the bus, they require the same amount of road space to transport the same number of passengers in the same amount of time. You have to have extremely short bus headways before the road space efficiency tilts back towards its favor.

Seems like you're basically saying "It doesn't matter because the same road can support either a bus or 20 cars." (1) This is a bad metric because it means everything is equivalent until traffic jam occurs. (Why stop at 20 cars? How about 2,000 cars?) (2) More importantly, everything cannot be equivalent because traffic jams do occur in any respectably-sized city. Having 20 cars instead of one bus absolutely does con…

You're making the same mistake as the author. What matters is how many people a lane can move in a given amount of time, not how large each burst of people is.

We stop at 20 cars in 10 minutes because that's the equivalent of the bus. If the bus ran twice as often (i.e. 5 minute headways), we'd have 40 cars in 10 minutes, but that's only one car every 15 seconds which is far from a congested state, especially with no traffic signals (like a rail/guideway based PRT or a hypothetical future self-driving system where cars coordinate with each other).

PRT is essentially just a bus system with a large number of small buses and a large number of routes as opposed to a traditional bus system with a small number of large buses and a small number of routes.

Re: Elon Musk doesn't understand geometry

#23

Post by fooker »

enraged_camel wrote: post #13
fooker wrote: post #5

Earlier quoted context omitted.

>(by pricing in externalities). In practice, this means someone pockets the change and nothing gets done about the so called externalities.

What do you mean? Can you give examples?

Suppose you want to force people to drive less — you increase gas prices with a tax.

Citing this extra tax, some lawmaker spends money on something completely irrelevant that was lobbied to them. Public transport is a fairly distant concern for most of them.

Oil companies increase crude prices to get on the gravy train, so does every other entity in the industry.

Car dealerships jack up prices because they want to maintain their profit levels.

Meanwhile middle class people who rely on cars get effed.

Re: Elon Musk doesn't understand geometry

#24

Post by [deleted] »

quantumwannabe wrote: post #22
yongjik wrote: post #21

Earlier quoted context omitted.

Seems like you're basically saying "It doesn't matter because the same road can support either a bus or 20 cars." (1) This is a bad metric because it means everything is equivalent until traffic jam occurs. (Why stop at 20 cars? How about 2,000 cars?) (2) More importantly, everything cannot be equivalent because traffic jams do occur in any respectably-sized city. Having 20 cars instead of one bus absolutely does con…

You're making the same mistake as the author. What matters is how many people a lane can move in a given amount of time, not how large each burst of people is. We stop at 20 cars in 10 minutes because that's the equivalent of the bus. If the bus ran twice as often (i.e. 5 minute headways), we'd have 40 cars in 10 minutes, but that's only one car every 15 seconds which is far from a congested state, especially with no…

[deleted]

Re: Elon Musk doesn't understand geometry

#25

Post by jcranmer »

quantumwannabe wrote: post #22
yongjik wrote: post #21

Earlier quoted context omitted.

Seems like you're basically saying "It doesn't matter because the same road can support either a bus or 20 cars." (1) This is a bad metric because it means everything is equivalent until traffic jam occurs. (Why stop at 20 cars? How about 2,000 cars?) (2) More importantly, everything cannot be equivalent because traffic jams do occur in any respectably-sized city. Having 20 cars instead of one bus absolutely does con…

You're making the same mistake as the author. What matters is how many people a lane can move in a given amount of time, not how large each burst of people is. We stop at 20 cars in 10 minutes because that's the equivalent of the bus. If the bus ran twice as often (i.e. 5 minute headways), we'd have 40 cars in 10 minutes, but that's only one car every 15 seconds which is far from a congested state, especially with no…

> but that's only one car every 15 seconds which is far from a congested state, especially with no traffic signals (like a rail/guideway based PRT or a hypothetical future self-driving system where cars coordinate with each other).

Not really. In the case of a guideway-based system, the minimum headway is determined by the time it takes to a) slow down to a safe diverging speed for the switch, b) physically pass over the switch at that speed and clear it, c) physically reset the switch to a different direction, and d) the following car has to be have sufficient distance to be able to stop in case the switch faults during step c. And you generally want to have some padding in there so that you can recover the schedule in case things go wrong. (Or you can dispense with switches entirely, in which case it's ruled by the amount of time vehicles have to dwell at a station for passengers to embark and disembark. Which, yeah, 15s is going to be too tight for that.)

The idea of using smart technology to improve capacity of roads by doing with safety margins is horrifying to me because a) the technology is really nowhere near that, b) the design is fundamentally hostile to pedestrians and cyclists and quite frankly anyone other than robodrivers, c) you still have the problem in urban environments that there's no room for grade-separated junctions, so the possible capacity gains are sharply limited, and d) safety margins exist for a reason! Just ask a certain submersible CEO (for whom you'll need a medium, for he recently stopped being biology and started being physics).

Re: Elon Musk doesn't understand geometry

#26

Post by caditinpiscinam »

quantumwannabe wrote: post #20
caditinpiscinam wrote: post #16

Earlier quoted context omitted.

I don't understand your point about time; how does 20 small vehicles not take up more room than a bus?

The bus and the 20 AVs have the same throughput (40 passengers in 10 minutes). While the AVs take up more physical space than the bus, they require the same amount of road space to transport the same number of passengers in the same amount of time. You have to have extremely short bus headways before the road space efficiency tilts back towards its favor.

I can see how that's true in the case of a single lane street: the 20 individual vehicles or the 1 bus both need one lane either way. But is it still true for higher volume cases? For example, I imagine that if you replaced a major subway line with a highway, the highway would have to be a lot larger to accommodate the same number of passengers in individual vehicles.

Re: Elon Musk doesn't understand geometry

#27

Post by josephcsible »

jcranmer wrote: post #7
pjkundert wrote: post #2

No, Elon does understand geometry — this author doesn’t understand the free market. On the rare occasion that the “public transit” busses sharing our roadways are full, they are indeed very efficient. Unfortunately - these situations are rare. The rest of the time, other solutions are vastly more desirable to the public. Simultaneously, these huge, lumbering 90%-empty beasts pile up traffic behind them, forcing massi…

You don't ride buses much do you? Of all the times I've ridden regular bus routes, there's only been one route where the bus being 90% empty would not be extremely atypical--and even then, that was only when I was picking up the bus during off-peak hours. More frequent have been the times where there being anything other than standing room available was the atypical situation. If you're in an urban environment at lea…

> Of all the times I've ridden regular bus routes, there's only been one route where the bus being 90% empty would not be extremely atypical

You're falling victim to the inspection paradox: https://towardsdatascience.com/the-inspection-paradox-is-eve...

Re: Elon Musk doesn't understand geometry

#28

Post by Freedom2 »

josephcsible wrote: post #27
jcranmer wrote: post #7

Earlier quoted context omitted.

You don't ride buses much do you? Of all the times I've ridden regular bus routes, there's only been one route where the bus being 90% empty would not be extremely atypical--and even then, that was only when I was picking up the bus during off-peak hours. More frequent have been the times where there being anything other than standing room available was the atypical situation. If you're in an urban environment at lea…

> Of all the times I've ridden regular bus routes, there's only been one route where the bus being 90% empty would not be extremely atypical You're falling victim to the inspection paradox: https://towardsdatascience.com/the-inspection-paradox-is-eve...

Interesting. What evidence do you have to back up your claim that the user has fallen victim to this paradox?

Re: Elon Musk doesn't understand geometry

#29

Post by josephcsible »

Freedom2 wrote: post #28
josephcsible wrote: post #27

Earlier quoted context omitted.

> Of all the times I've ridden regular bus routes, there's only been one route where the bus being 90% empty would not be extremely atypical You're falling victim to the inspection paradox: https://towardsdatascience.com/the-inspection-paradox-is-eve...

Interesting. What evidence do you have to back up your claim that the user has fallen victim to this paradox?

Using your experience as a passenger to gauge how full buses usually are is about as straightforward of an example of that paradox as you could ask for. As an extreme example, imagine there are 10 bus routes, 9 of which are always empty and 1 of which is always full. If you surveyed every passenger, they'd tell you that 100% of the buses they've ever been on are full, but in reality, only 10% of the buses are.

Re: Elon Musk doesn't understand geometry

#30

Post by rsynnott »

quantumwannabe wrote: post #22
yongjik wrote: post #21

Earlier quoted context omitted.

Seems like you're basically saying "It doesn't matter because the same road can support either a bus or 20 cars." (1) This is a bad metric because it means everything is equivalent until traffic jam occurs. (Why stop at 20 cars? How about 2,000 cars?) (2) More importantly, everything cannot be equivalent because traffic jams do occur in any respectably-sized city. Having 20 cars instead of one bus absolutely does con…

You're making the same mistake as the author. What matters is how many people a lane can move in a given amount of time, not how large each burst of people is. We stop at 20 cars in 10 minutes because that's the equivalent of the bus. If the bus ran twice as often (i.e. 5 minute headways), we'd have 40 cars in 10 minutes, but that's only one car every 15 seconds which is far from a congested state, especially with no…

> We stop at 20 cars in 10 minutes because that's the equivalent of the bus.

I think you're underestimating the capacity of a bus system significantly. I live in Dublin, which is a city of about 1.5 million people, not super-dense, hardly the world's greatest metropolis. The double-decker buses used almost exclusively in the Dublin transport system hold 90 people (from time to time Dublin bus experiments with bendy buses, but they tend to get stuck on roundabouts). Let's say the average car holds 1.5 people (I think this is generous, it's probably closer to one, but let's go with it). So a bus is equiv to 60 cars.

I can think of a few streets nearby which have stops for ~20 bus routes, with other routes running through them but not stopping. Some will be every-20-minutes routes, but some will be closer to every-five-minutes at peak. At peak time, there will be multiple buses per minute on many streets. You will see buses queuing up behind each other to load and unload. There is _no way_ that the equiv capacity in cars could even _fit_ on the road, even if traffic wasn't a concern.

These, by the way, are normal bus routes, not BRT; that would be even worse.

Here's the practical equivalent of 240 cars embodied in buses (plus 272 in the tram): https://s3.eu-west-1.amazonaws.com/prod-mh-ireland/607c5cf1-... - It's hard to see how you'd fit those cars in the equiv space. At peak times, all of those buses will be full.

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