> Why are different modes of travel's safety measured in passenger mile instead of passenger hours?
Because it's really the only sensible way to compare different forms of transportation.
Imagine a teleportation device with an accidental death rate of 1 per 10 trillion miles. But it only takes 2ms to operate (regardless of distance), so the death rate measured in hours would be horrible.
Compare that to covered wagons. Per mile, they're quite dangerous—going on a long trip in one might mean a 1 in 10 chance of death. But they're also extremely slow. So measuring death in terms of hours would make them look safe.
From a safety perspective, which would you rather use?
Because it's really the only sensible way to compare different forms of transportation.
Imagine a teleportation device with an accidental death rate of 1 per 10 trillion miles. But it only takes 2ms to operate (regardless of distance), so the death rate measured in hours would be horrible.
Compare that to covered wagons. Per mile, they're quite dangerous—going on a long trip in one might mean a 1 in 10 chance of death. But they're also extremely slow. So measuring death in terms of hours would make them look safe.
From a safety perspective, which would you rather use?