There are three main ways in which risk of fatality of a certain mode of travel can be measured: Deaths per billion typical journeys taken, deaths per billion hours traveled, or deaths per billion kilometers traveled.
The following table displays these statistics for the United Kingdom 1990–2000. Note that aviation safety does not include the transportation to the airport.
The first two statistics are computed for typical travels for respective forms of transport, so they cannot be used directly to compare risks related to different forms of transport in a particular travel “from A to B”. For example: according to statistics, a typical flight from Los Angeles to New York will carry a larger risk factor than a typical car travel from home to office. But a car travel from Los Angeles to New York would not be typical. It would be as large as several dozens of typical car travels, and associated risk will be larger as well. Because the journey would take a much longer time, the overall risk associated by making this journey by car will be higher than making the same journey by air, even if each individual hour of car travel can be less risky than an hour of flight.
It is therefore important to use each statistic in a proper context. When it comes to a question about risks associated with a particular long-range travel from one city to another, the most suitable statistic is the third one, thus giving a reason to name air travel as the safest form of long-range transportation. However, if the availability of an air option makes an otherwise inconvenient journey possible, then this argument loses some of its force.
Aviation industry insurers base their calculations on the deaths per journey statistic while the aviation industry itself generally uses the deaths per kilometre statistic in press releases.
Since 1997 the number of fatal air accidents has been no more than 1 for every 2,000,000,000 person-miles flown (e.g., 100 people flying a plane for 1,000 miles (1,600 km) counts as 100,000 person-miles, making it comparable with methods of transportation with different numbers of passengers, such as one person driving an automobile for 100,000 miles (160,000 km), which is also 100,000 person-miles), and thus one of the safest modes of transportation when measured by distance traveled.