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Is it really wasteful? It seems like it is an ever moving system. In terms of people capacity it seems it would carry more by being always flowing vs a stopping

by jv22222 10y ago

Is it really wasteful? It seems like it is an ever moving system. In terms of people capacity it seems it would carry more by being always flowing vs a stopping starting transit system.

osdiab 10y ago
The amount of people that can fit in 1 car is roughly maxes out at 4-7 people, depending on the car. There needs to be enough spacing between each car so that in the case of a failure, cars have space to brake to a stop without catapulting the people in it, or causing them to become overly nauseous. So there's going to be a decent amounnt of spacing between each car. The number of people that can fit on 1 bus can hit in the ballpark of 50 people, so we're getting a roughly 10x capacity boost here. You lose the "ever-moving system" benefit doing this, but I highly doubt some stopping and starting would lead to an order of magnitude slower speed. Now, the number of people that can fit on 1 SF BART train is in the realm of 10 cars * 200 = 2000 people per train. The spacing is not going to be on the order of 100x longer than in the individual car case, and the starting-stopping speed is going to be not a bit slower than the bus case. I'll let you work out the math on that, but it's not even orders of magnitude close. Don't need to be a "visionary" to see that.
- Retric 10y ago
  A well managed train system can manage 1 car per line per 5 minutes. 2000 * 60 / 5 = 24,000 people per hour. Highways can handle 2,000 - 2200 vehicles per lane or so at the low end 1/12 but that's very much an edge case. Most lines are closer to one train every 20 minutes and you can average 3 people per car which makes them equivalent. The real issue is not highways, but what happens when people try and get off or onto them. It's possible but rare to do this well.
  - tigershark 10y ago
    Do you mean a shitty managed train system, right? In London at peak time there is one train every two minutes, in Moscow one per minute. One train every 5 minutes is the off peak frequency in London when you are actually complaining that you are waiting too long.
    - deleted 10y ago
      [deleted]
    - Retric 10y ago
      At the peak times for the most used stations there is a car that frequently sure, but if use look at the overall system they don't send anywhere close to 60 * 24 = 1440 trains past every station in each direction per day. Further trains going to different stations often share the same track because you need more throughput in the city center than at the furthest stations. But, just because the edge stations get less use does not mean the track is cheaper to construct.
      - osdiab 10y ago
        The max throughout is the number that we should care about - they provide fewer cars per minute not because they're physically incapable of doing it, just because there isn't demand. And it would be the same in a car-centric situation as well - lower throughput in off hours.
        Retric 10y ago
        Having the ability to send 1 billion people from A to B is useless unless there is actual demand to send 1 billion people from A to B. Similarly, not all stations get anywhere close to the same demand, but you need to build a large network or the peak demand is less. Thus, measuring the network is what's important not the 'best case' subset of a few most heavily used stations. Further, roads and bridges do get used from 2-4 AM when subway systems are generally not operating, so it's the use over the full day that's important not just peak usage.
  - osdiab 10y ago
    It's less of an edge case than you may think, given solo ridership numbers here in the USA. 75% commute alone. https://www.census.gov/hhes/commuting/files/2014/acs-32.pdf https://www.census.gov/hhes/commuting/files/2014/acs-32.pdf
    - Retric 10y ago
      The average over the full US is kind of meaningless as most areas don't have traffic problems. It's only large city's that actually matter in this assessment. On page 4, 2006: 80% used a carpool or single occupancy car. 2013: 76% used a carpool or single occupancy car which is counter to their narrative. Further, metro areas are rather large, I commute less than 3 miles on secondary roads in the DC metro area from just outside the beltway to just inside of it and encounter approximately zero traffic.

by jv22222 10y ago

Is it really wasteful? It seems like it is an ever moving system. In terms of people capacity it seems it would carry more by being always flowing vs a stopping starting transit system.

osdiab 10y ago

The amount of people that can fit in 1 car is roughly maxes out at 4-7 people, depending on the car. There needs to be enough spacing between each car so that in the case of a failure, cars have space to brake to a stop without catapulting the people in it, or causing them to become overly nauseous. So there's going to be a decent amounnt of spacing between each car. The number of people that can fit on 1 bus can hit in the ballpark of 50 people, so we're getting a roughly 10x capacity boost here. You lose the "ever-moving system" benefit doing this, but I highly doubt some stopping and starting would lead to an order of magnitude slower speed. Now, the number of people that can fit on 1 SF BART train is in the realm of 10 cars * 200 = 2000 people per train. The spacing is not going to be on the order of 100x longer than in the individual car case, and the starting-stopping speed is going to be not a bit slower than the bus case. I'll let you work out the math on that, but it's not even orders of magnitude close. Don't need to be a "visionary" to see that.

Retric 10y ago
A well managed train system can manage 1 car per line per 5 minutes. 2000 * 60 / 5 = 24,000 people per hour. Highways can handle 2,000 - 2200 vehicles per lane or so at the low end 1/12 but that's very much an edge case. Most lines are closer to one train every 20 minutes and you can average 3 people per car which makes them equivalent. The real issue is not highways, but what happens when people try and get off or onto them. It's possible but rare to do this well.
- tigershark 10y ago
  Do you mean a shitty managed train system, right? In London at peak time there is one train every two minutes, in Moscow one per minute. One train every 5 minutes is the off peak frequency in London when you are actually complaining that you are waiting too long.
  - deleted 10y ago
    [deleted]
  - Retric 10y ago
    At the peak times for the most used stations there is a car that frequently sure, but if use look at the overall system they don't send anywhere close to 60 * 24 = 1440 trains past every station in each direction per day. Further trains going to different stations often share the same track because you need more throughput in the city center than at the furthest stations. But, just because the edge stations get less use does not mean the track is cheaper to construct.
    - osdiab 10y ago
      The max throughout is the number that we should care about - they provide fewer cars per minute not because they're physically incapable of doing it, just because there isn't demand. And it would be the same in a car-centric situation as well - lower throughput in off hours.
      - Retric 10y ago
        Having the ability to send 1 billion people from A to B is useless unless there is actual demand to send 1 billion people from A to B. Similarly, not all stations get anywhere close to the same demand, but you need to build a large network or the peak demand is less. Thus, measuring the network is what's important not the 'best case' subset of a few most heavily used stations. Further, roads and bridges do get used from 2-4 AM when subway systems are generally not operating, so it's the use over the full day that's important not just peak usage.
- osdiab 10y ago
  It's less of an edge case than you may think, given solo ridership numbers here in the USA. 75% commute alone. https://www.census.gov/hhes/commuting/files/2014/acs-32.pdf https://www.census.gov/hhes/commuting/files/2014/acs-32.pdf
  - Retric 10y ago
    The average over the full US is kind of meaningless as most areas don't have traffic problems. It's only large city's that actually matter in this assessment. On page 4, 2006: 80% used a carpool or single occupancy car. 2013: 76% used a carpool or single occupancy car which is counter to their narrative. Further, metro areas are rather large, I commute less than 3 miles on secondary roads in the DC metro area from just outside the beltway to just inside of it and encounter approximately zero traffic.