I don't find per mile all that useful when comparing modes of transportation for safety, because for some modes of transportation the risk of a trip doesn't really depend much on the distance.
To give an extreme example, imagine someone starts passenger service from Earth to some planet in the Andromeda galaxy. Each flight carries 100 people. Once the warp field is stabilized the rest of the trip is 100% safe. However when the warp field is turned on their is a 99% chance that it will collapse rather than stabilize, which will destroy the ship and kill everyone aboard.
These Andromeda flights are 5 orders of magnitude safer than commercial air travel when measures by passenger fatalities per mile.
To give an extreme example, imagine someone starts passenger service from Earth to some planet in the Andromeda galaxy. Each flight carries 100 people. Once the warp field is stabilized the rest of the trip is 100% safe. However when the warp field is turned on their is a 99% chance that it will collapse rather than stabilize, which will destroy the ship and kill everyone aboard.
These Andromeda flights are 5 orders of magnitude safer than commercial air travel when measures by passenger fatalities per mile.