&gt; Why are different modes of travel&#x27;s safety measured in passenger mile instead of passenger hours?<p>Because it&#x27;s really the only sensible way to compare different forms of transportation.<p>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.<p>Compare that to covered wagons. Per mile, they&#x27;re quite dangerous—going on a long trip in one might mean a 1 in 10 chance of death. But they&#x27;re also extremely slow. So measuring death in terms of hours would make them look safe.<p>From a safety perspective, which would you rather use?