4 ms·

Maybe we'll get lucky and perfectly safe self driving cars will solve the problem once and for all in 20 years?

statguy 8y ago
A Subway line will always be an order of magnitude more efficient than a system where each individual is in a separate vehicle, self driving or not.
- seanmcdirmid 8y ago
  Depends on utilization and capacity needs. A subway is an incredibly much more inefficient use of capital if it only needs to handle a few passengers an hour between fixed points, let alone non fixed ones.
  - statguy 8y ago
    Sure, it dosen't make sense to build subway lines to replace all roads/highways. However, as bobthepanda's comment says, once the demand on a route exceeds a threshold, mass transit wins by a mile.
    - seanmcdirmid 8y ago
      Yes, but parent used an unqualified “always” without any room for additional context.
s0rce 8y ago
I can't see even self-driving cars coming close to the transportation efficiency of light/heavy rail. You just can't fit people close together if each person is in big metal box. Also, self-driving cars would likely increase the amount of time people would tolerate in a vehicle as you can do other things so more people would be willing to sit in traffic and commute times might not even improve.
- SomewhatLikely 8y ago
  But what about all the empty track between trains? When you consider that, it starts to level out. I'd be very interested in actual numbers though. Edit: Discussion here using quick estimates seems to show rail still wins: https://alankandel.scienceblog.com/2014/01/11/rails-vs-roads-for-value-utilization-emissions-savings-difference-like-night-and-day/ https://alankandel.scienceblog.com/2014/01/11/rails-vs-roads...
  - adrianN 8y ago
    How many lanes of self driving cars cars do you think it takes to replace a subway line at full capacity? More than you think. See London's Victoria line for reference https://www.youtube.com/watch?v=ASKof4CR2SE https://www.youtube.com/watch?v=ASKof4CR2SE Trains run every ninety seconds or so and are packed during rush hour.
melling 8y ago
Will these cars go 100-300 mph? At some point, shouldn’t maglev trains and subways be practical? https://www.businesstoday.in/current/world/china-successfully-tests-maglev-train-prototype-with-160kmph-top-speed/story/277580.html https://www.businesstoday.in/current/world/china-successfull...
- stephengillie 8y ago
  Trains run 25mph in most cities. Like another poster commented, Link Light Rail takes about 2x as long as driving.
  - prolikewh0a 8y ago
    Tukwila -> Westlake (11 stops? I think?) takes around 45-50 minutes. My bus from the same area takes ~20 minutes to the same stop. The bus doesn't run on weekends, so I have to take the light rail and it's so slow.
    - stephengillie 8y ago
      Via I-5, this commute[0] is 13.6 miles. Via SR-99, it's 13.1 miles. In Friday morning traffic, the route can take 30-50 minutes by car. On Saturday nights, it can take 15 minutes. If you can get 40 MPG and pay $3.40 per gallon, this could cost just $1.27 in gasoline, instead of $2.50 to a train or bus company. [0]https://goo.gl/maps/iyZEKttcBFo https://goo.gl/maps/iyZEKttcBFo Edit: Multiply not divide. ;)
  - adrianN 8y ago
    Trains in Berlin can go 80km/h.
  - melling 8y ago
    Yes, I already know that. It’s completely irrelevant to my comment. Why did you bring it up? Maglev trains won’t be running at 25 mph.
bryanlarsen 8y ago
Self driving will have an impact like Uber: slightly decreasing ownership rates but massively increasing traffic.
bobthepanda 8y ago
Self driving cars are limited by capacity; cars today have an average occupancy hovering around one and a half. Because of this a free-flowing, 55MPH highway lane has capacity for about 2-3K per hour. To give those numbers some context, when Seattle's Link Light Rail builds out ST2 in 2021, capacity will be 14.4K per hour; and this is running a ordinary schedule of every four minutes. The New York City Subway at its busiest scheduled section runs much longer trains every two minutes, at a capacity of 75K per hour. That's with 1930's signalling - with modern signalling, they could run trains every 90 seconds, for a capacity of 100k per hour. And that's just on two tracks. Cars are really space inefficient because you need an engine and a fuel tank for a small group of people. Trains and buses have the advantage of fitting more seats in the same area, and then having people stand on top of that.
- djrogers 8y ago
  > That's with 1930's signalling - with modern signalling, they could run trains every 90 seconds, for a capacity of 100k per hour. And that's just on two tracks. That's an extremely optimistic number - running a train every 90 seconds would leave people basically no time to get on or off the train, and ingress/egress gets harder as platforms get more crowded.
  - bobthepanda 8y ago
    90s is achieved on many subway lines today. Ingress/egress is mostly a function of getting the people farthest from the doors out the train and packing people in, but there are subway lines that effectively manage this at 90s. Paris Metro Lines 1 and 14 already run at this headway. That being said, it is possible for platforms to become so congested that they actually start impacting headways; the Lexington Av Line (4/5/6) in New York had this issue until recently because it was carrying more than the daily riderships of Chicago, Boston, and San Francisco's entire systems.

A Subway line will always be an order of magnitude more efficient than a system where each individual is in a separate vehicle, self driving or not.

seanmcdirmid 8y ago
Depends on utilization and capacity needs. A subway is an incredibly much more inefficient use of capital if it only needs to handle a few passengers an hour between fixed points, let alone non fixed ones.
- statguy 8y ago
  Sure, it dosen't make sense to build subway lines to replace all roads/highways. However, as bobthepanda's comment says, once the demand on a route exceeds a threshold, mass transit wins by a mile.
  - seanmcdirmid 8y ago
    Yes, but parent used an unqualified “always” without any room for additional context.

s0rce 8y ago

I can't see even self-driving cars coming close to the transportation efficiency of light/heavy rail. You just can't fit people close together if each person is in big metal box. Also, self-driving cars would likely increase the amount of time people would tolerate in a vehicle as you can do other things so more people would be willing to sit in traffic and commute times might not even improve.

SomewhatLikely 8y ago
But what about all the empty track between trains? When you consider that, it starts to level out. I'd be very interested in actual numbers though. Edit: Discussion here using quick estimates seems to show rail still wins: https://alankandel.scienceblog.com/2014/01/11/rails-vs-roads-for-value-utilization-emissions-savings-difference-like-night-and-day/ https://alankandel.scienceblog.com/2014/01/11/rails-vs-roads...
- adrianN 8y ago
  How many lanes of self driving cars cars do you think it takes to replace a subway line at full capacity? More than you think. See London's Victoria line for reference https://www.youtube.com/watch?v=ASKof4CR2SE https://www.youtube.com/watch?v=ASKof4CR2SE Trains run every ninety seconds or so and are packed during rush hour.

melling 8y ago

Will these cars go 100-300 mph? At some point, shouldn’t maglev trains and subways be practical? https://www.businesstoday.in/current/world/china-successfully-tests-maglev-train-prototype-with-160kmph-top-speed/story/277580.html https://www.businesstoday.in/current/world/china-successfull...

stephengillie 8y ago
Trains run 25mph in most cities. Like another poster commented, Link Light Rail takes about 2x as long as driving.
- prolikewh0a 8y ago
  Tukwila -> Westlake (11 stops? I think?) takes around 45-50 minutes. My bus from the same area takes ~20 minutes to the same stop. The bus doesn't run on weekends, so I have to take the light rail and it's so slow.
  - stephengillie 8y ago
    Via I-5, this commute[0] is 13.6 miles. Via SR-99, it's 13.1 miles. In Friday morning traffic, the route can take 30-50 minutes by car. On Saturday nights, it can take 15 minutes. If you can get 40 MPG and pay $3.40 per gallon, this could cost just $1.27 in gasoline, instead of $2.50 to a train or bus company. [0]https://goo.gl/maps/iyZEKttcBFo https://goo.gl/maps/iyZEKttcBFo Edit: Multiply not divide. ;)
- adrianN 8y ago
  Trains in Berlin can go 80km/h.
- melling 8y ago
  Yes, I already know that. It’s completely irrelevant to my comment. Why did you bring it up? Maglev trains won’t be running at 25 mph.

bryanlarsen 8y ago

Self driving will have an impact like Uber: slightly decreasing ownership rates but massively increasing traffic.

bobthepanda 8y ago

Self driving cars are limited by capacity; cars today have an average occupancy hovering around one and a half. Because of this a free-flowing, 55MPH highway lane has capacity for about 2-3K per hour. To give those numbers some context, when Seattle's Link Light Rail builds out ST2 in 2021, capacity will be 14.4K per hour; and this is running a ordinary schedule of every four minutes. The New York City Subway at its busiest scheduled section runs much longer trains every two minutes, at a capacity of 75K per hour. That's with 1930's signalling - with modern signalling, they could run trains every 90 seconds, for a capacity of 100k per hour. And that's just on two tracks. Cars are really space inefficient because you need an engine and a fuel tank for a small group of people. Trains and buses have the advantage of fitting more seats in the same area, and then having people stand on top of that.

djrogers 8y ago
> That's with 1930's signalling - with modern signalling, they could run trains every 90 seconds, for a capacity of 100k per hour. And that's just on two tracks. That's an extremely optimistic number - running a train every 90 seconds would leave people basically no time to get on or off the train, and ingress/egress gets harder as platforms get more crowded.
- bobthepanda 8y ago
  90s is achieved on many subway lines today. Ingress/egress is mostly a function of getting the people farthest from the doors out the train and packing people in, but there are subway lines that effectively manage this at 90s. Paris Metro Lines 1 and 14 already run at this headway. That being said, it is possible for platforms to become so congested that they actually start impacting headways; the Lexington Av Line (4/5/6) in New York had this issue until recently because it was carrying more than the daily riderships of Chicago, Boston, and San Francisco's entire systems.