[apendleton]

I'd argue that deaths per mile is also misleading, however, as it misstates the actual benefit; people don't directly benefit from a particular number of miles, but rather from a particular set of trips, whose length will tend to vary by mode. People who choose a car-oriented lifestyle will tend, on average, to make longer trips than those who choose lifestyles built around transportation by walking, biking, or using transit, but I would argue that the urban cyclist biking two miles to work derives the same benefit (getting from home to work) as the suburban car commuter driving twenty miles. For comparing cars to bikes, in particular, the relative safety depends on whether you go with a per-mile or per-trip metric, with the winners being car and bike, respectively.

[jeffdavis]

I mostly agree, but that's true any time you wrap a complex problem up into a single number. I am merely arguing that, if we pick a single number, deaths-per-passenger-mile is much better than deaths-per-licensed-driver.

I guess you are saying that deaths-per-trip is an even better number. That would be interesting to see, I agree, but as an additional number, not a replacement.