3 ms·

I think it makes a lot more sense to look at risk per time, because it's basically the same thing as risk per trip, and that's what I really care about. If you

I think it makes a lot more sense to look at risk per time, because it's basically the same thing as risk per trip, and that's what I really care about. If you tell me I can fly to Mars in a few days on a brachistochrone torchship and it's safer per mile than any other mode of transport, you may be right, and a few days cooped up in a cramped cabin might be a small price to pay for such an exotic vacation destination, but that risk calculus is really very misleading. The distance involved is so vast that per mile it could be an absurdly low figure by any terrestrial standard while still carrying an absurdly high (by the same standards) risk of death during the trip. In other words, if the odds are e.g. 1 in 10 that the trip will kill me, I don't give a shit how low the risk per mile is.

apendleton 6y ago
This seems like a mode of comparison that's disconnected from actual utility. The distance comparison lets me consider a scenario like "I live in Washington, DC. I want to go to New York. I can choose to either get there by plane or car, and I want to know which is safer." This seems like a real, sensible thing to contemplate. The time comparison is "I live in Washington, DC and want to go... to wherever it is that happens to be an hour away from me by whatever mode of transport I happen to be using (so, either New York or someplace outside of Baltimore) and I want to know which is safer"... but I can't for the life of me fathom why the second is a tradeoff anyone would actually be forced to consider. People generally travel with the objective of getting from some specific place to some other specific place.
- caconym_ 6y ago
  Most people do, in fact, have specific travel time expectations for specific kinds of trips. Going away for a long weekend? Probably you're thinking 1-5 hours, whether you're driving or flying. A week or two? Maybe 5-10 hours. Going to the store? 5-15 minutes. Physical distance doesn't matter at all, because it's abstracted away by the transportation technology. All we care about is cost (time and money), availability of destinations, and risk; and since distance doesn't matter, it really can't be risk per distance that we care about. In practice, no mode of transportation anywhere near as risky per time or per trip as my Mars example is ever going to become mainstream. The point of it is to demonstrate how absurd risk per distance is as a way of getting at a practical and meaningful assessment of travel risk, and we have to go outside of existing mainstream transportation options to see that absurdity because all the existing options must be extremely low risk by any measure or they wouldn't exist. The majority of consumers won't tolerate 1 in 10, 1 in 100, or even 1 in 1000 odds of death per trip.
- ponker 6y ago
  This assumes that people decide the destination before deciding the mode of transport. In my experience this isn't true, specifically with the 737 MAX. I had a 4-night trip booked with my family to Seattle from San Francisco on a 737 MAX and cancelled it when all that shit went down. Rather than driving that weekend to Seattle we drove to Yosemite because I wasn't going to drive 12 hours to Seattle. In terms of total travel time (time to drive to airport, check in, and fly) the travel time was about the same to Yosemite as to Seattle but the mileage was obviously much less.
  - deleted 6y ago
    [deleted]
- tsimionescu 6y ago
  I think there are actually two modes of deciding this, and the two different calculations make sense for each mode. Sometimes you need to be in a specific city - say, a work trip, or public event, or life event etc. Then, the question you want to ask is "which vehicle will take me there in the safest manner", and plane will likely win (assuming large distance). Other times, you are deciding on a vacation destination. Here you often have a more-or-less fixed time budget, but a flexible destination, and the question can become "what is the safest trip I can take that will last between, say, 5-10h?" ( I could get to NY by plane, or to Vienna by train, or to the Golden Sands by car in roughly that time). In this case, trains and other mass transports besides planes may well win out in safety.
- gorgoiler 6y ago
  People travel to places because it is tractable to get there in a reasonable amount of time. In the 17th century, I would walk to my local knife sharpener. In the 21st century, I can take a train to Soho to visit a superior specialist. Both trips take a few hours via two different modes of transport. The fact that one covers more distance is immaterial. They are comparable by the fact they can both be completed in an afternoon. (Ironically, our modern era provides a third option: cycle to the local specialist. Cycling with a bag full of knives — even blunt ones — is way too risky.)
taneq 6y ago
This approach really only makes sense if you're traveling for fun. If you need to get to a particular place then risk per time is absolutely not the same as risk per trip, because the distance you need to travel is fixed.
- caconym_ 6y ago
  If you need to go somewhere with a realistic choice between e.g. driving and flying (which seems quite rare), risk per distance is fine for choosing one or the other via risk per trip. But the implication of it being a realistic choice is that the travel times are comparable, meaning risk per time will also be comparable, and risk per time has the benefit of not producing absurd answers for edge cases like my Mars example. Every new world-shrinking transportation innovation has changed the distribution of things in the world and increased the distance society expects us to travel on various kinds of "required" trips. That's because time and money are more important than distance in deciding whether a trip is worth it.
Sebb767 6y ago
> In other words, if the odds are e.g. 1 in 10 that the trip will kill me, I don't give a shit how low the risk per mile is. The average distance to mars is about 225 million km, so that would be one accident about every 2,2 billion km or 0.45 deaths per km, which is a bit deadlier than buses and 9 times as deadly as planes. Gives some perspective on how save planes actually are.
- zrobotics 6y ago
  You might want to check your figures- 1 death/2.2e9 km is 4.5e-10 deaths per km. The 0.45/km figure is way out, for that to be the case there would need to be roughly 1.1billion deaths per 2.2 billion km.
  - Sebb767 6y ago
    Yes, this was in deaths per billion km - sorry, should've specified.

apendleton 6y ago

This seems like a mode of comparison that's disconnected from actual utility. The distance comparison lets me consider a scenario like "I live in Washington, DC. I want to go to New York. I can choose to either get there by plane or car, and I want to know which is safer." This seems like a real, sensible thing to contemplate. The time comparison is "I live in Washington, DC and want to go... to wherever it is that happens to be an hour away from me by whatever mode of transport I happen to be using (so, either New York or someplace outside of Baltimore) and I want to know which is safer"... but I can't for the life of me fathom why the second is a tradeoff anyone would actually be forced to consider. People generally travel with the objective of getting from some specific place to some other specific place.

caconym_ 6y ago
Most people do, in fact, have specific travel time expectations for specific kinds of trips. Going away for a long weekend? Probably you're thinking 1-5 hours, whether you're driving or flying. A week or two? Maybe 5-10 hours. Going to the store? 5-15 minutes. Physical distance doesn't matter at all, because it's abstracted away by the transportation technology. All we care about is cost (time and money), availability of destinations, and risk; and since distance doesn't matter, it really can't be risk per distance that we care about. In practice, no mode of transportation anywhere near as risky per time or per trip as my Mars example is ever going to become mainstream. The point of it is to demonstrate how absurd risk per distance is as a way of getting at a practical and meaningful assessment of travel risk, and we have to go outside of existing mainstream transportation options to see that absurdity because all the existing options must be extremely low risk by any measure or they wouldn't exist. The majority of consumers won't tolerate 1 in 10, 1 in 100, or even 1 in 1000 odds of death per trip.
ponker 6y ago
This assumes that people decide the destination before deciding the mode of transport. In my experience this isn't true, specifically with the 737 MAX. I had a 4-night trip booked with my family to Seattle from San Francisco on a 737 MAX and cancelled it when all that shit went down. Rather than driving that weekend to Seattle we drove to Yosemite because I wasn't going to drive 12 hours to Seattle. In terms of total travel time (time to drive to airport, check in, and fly) the travel time was about the same to Yosemite as to Seattle but the mileage was obviously much less.
- deleted 6y ago
  [deleted]
tsimionescu 6y ago
I think there are actually two modes of deciding this, and the two different calculations make sense for each mode. Sometimes you need to be in a specific city - say, a work trip, or public event, or life event etc. Then, the question you want to ask is "which vehicle will take me there in the safest manner", and plane will likely win (assuming large distance). Other times, you are deciding on a vacation destination. Here you often have a more-or-less fixed time budget, but a flexible destination, and the question can become "what is the safest trip I can take that will last between, say, 5-10h?" ( I could get to NY by plane, or to Vienna by train, or to the Golden Sands by car in roughly that time). In this case, trains and other mass transports besides planes may well win out in safety.
gorgoiler 6y ago
People travel to places because it is tractable to get there in a reasonable amount of time. In the 17th century, I would walk to my local knife sharpener. In the 21st century, I can take a train to Soho to visit a superior specialist. Both trips take a few hours via two different modes of transport. The fact that one covers more distance is immaterial. They are comparable by the fact they can both be completed in an afternoon. (Ironically, our modern era provides a third option: cycle to the local specialist. Cycling with a bag full of knives — even blunt ones — is way too risky.)

taneq 6y ago

This approach really only makes sense if you're traveling for fun. If you need to get to a particular place then risk per time is absolutely not the same as risk per trip, because the distance you need to travel is fixed.

caconym_ 6y ago
If you need to go somewhere with a realistic choice between e.g. driving and flying (which seems quite rare), risk per distance is fine for choosing one or the other via risk per trip. But the implication of it being a realistic choice is that the travel times are comparable, meaning risk per time will also be comparable, and risk per time has the benefit of not producing absurd answers for edge cases like my Mars example. Every new world-shrinking transportation innovation has changed the distribution of things in the world and increased the distance society expects us to travel on various kinds of "required" trips. That's because time and money are more important than distance in deciding whether a trip is worth it.

Sebb767 6y ago

> In other words, if the odds are e.g. 1 in 10 that the trip will kill me, I don't give a shit how low the risk per mile is. The average distance to mars is about 225 million km, so that would be one accident about every 2,2 billion km or 0.45 deaths per km, which is a bit deadlier than buses and 9 times as deadly as planes. Gives some perspective on how save planes actually are.

zrobotics 6y ago
You might want to check your figures- 1 death/2.2e9 km is 4.5e-10 deaths per km. The 0.45/km figure is way out, for that to be the case there would need to be roughly 1.1billion deaths per 2.2 billion km.
- Sebb767 6y ago
  Yes, this was in deaths per billion km - sorry, should've specified.