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There are arguments against measuring crash rates by “number per vehicle miles traveled” and instead by “number per vehicle hours traveled.” VMT is a product of

There are arguments against measuring crash rates by “number per vehicle miles traveled” and instead by “number per vehicle hours traveled.” VMT is a product of speed and time, and thus a fatalities-per-VMT metric will nearly always show the faster routes to be safer. But compare spending 20 minutes traveling 10 miles on a local street, vs 10 minutes traveling 10 miles on a freeway. Both are considered equally safe using a fatalities-per-VMT model. But in the former, you’ve stayed safe for a longer portion of your life. (See http://pedshed.net/?p=1050 http://pedshed.net/?p=1050) Using that metric would make that Boeing far less safe compared with driving.

Pristina 8y ago
But you travel to get somewhere not to be in a vehicle for X amount of time. So why would any metrics besides per-distance be more relevant.
- heliodor 8y ago
  As a traveler, I care about the trip, not the time nor the distance. If I take this trip, what's my probability of dying if I fly it versus drive it. Airplane travel have fixed segments (takeoff and landing, ascent, descent) and variable segments (the coasting phase that varies by distance traveled). Car travel is only the variable segment. Hard to compare apples to oranges.
LoSboccacc 8y ago
> measuring crash rates by “number per vehicle miles traveled” and instead by “number per vehicle hours traveled.” there's another issue, which is plane risk is uneven during their journey, so a type that does half the flights but twice the distance on average will end up almost 1.5 times as safe all other things being equal. this source claim 45% crashes happening on takeoff and landing which are a minimal percentage of travel if you measure risk by mile or hour: https://eu.usatoday.com/story/travel/columnist/cox/2013/08/26/ask-the-captain-danger-takeoffs-landings/2693891/ https://eu.usatoday.com/story/travel/columnist/cox/2013/08/2... a way to normalize that would have to use "number per flights" but then you'd get trains, with their multi-stop journeys, skewing the numbers the other way.
arcticfox 8y ago
That argument seems flawed to the point of absurdity. Two extreme examples showcase this: 1) a teleporter with the exact same risk as driving 20min on local streets or 10min on the highway would be the worst thing ever invented. In reality, 100% of people would choose it unless they were intentionally wanting to spend time driving 2) A 100% safe ridable snail would be the ideal form of transit, given that you'd spend your whole life safely trying to get somewhere.

Pristina 8y ago

But you travel to get somewhere not to be in a vehicle for X amount of time. So why would any metrics besides per-distance be more relevant.

heliodor 8y ago
As a traveler, I care about the trip, not the time nor the distance. If I take this trip, what's my probability of dying if I fly it versus drive it. Airplane travel have fixed segments (takeoff and landing, ascent, descent) and variable segments (the coasting phase that varies by distance traveled). Car travel is only the variable segment. Hard to compare apples to oranges.

LoSboccacc 8y ago

> measuring crash rates by “number per vehicle miles traveled” and instead by “number per vehicle hours traveled.” there's another issue, which is plane risk is uneven during their journey, so a type that does half the flights but twice the distance on average will end up almost 1.5 times as safe all other things being equal. this source claim 45% crashes happening on takeoff and landing which are a minimal percentage of travel if you measure risk by mile or hour: https://eu.usatoday.com/story/travel/columnist/cox/2013/08/26/ask-the-captain-danger-takeoffs-landings/2693891/ https://eu.usatoday.com/story/travel/columnist/cox/2013/08/2... a way to normalize that would have to use "number per flights" but then you'd get trains, with their multi-stop journeys, skewing the numbers the other way.

arcticfox 8y ago

That argument seems flawed to the point of absurdity. Two extreme examples showcase this: 1) a teleporter with the exact same risk as driving 20min on local streets or 10min on the highway would be the worst thing ever invented. In reality, 100% of people would choose it unless they were intentionally wanting to spend time driving 2) A 100% safe ridable snail would be the ideal form of transit, given that you'd spend your whole life safely trying to get somewhere.