The problem: Each of the modes uses a different set of denominators for evaluating changes in safety risk.
This variety makes aggregation or comparison unworkable, which limits our ability to find differences in risk. It can mask important safety risks, and limits the public's understanding of the relative risk associated with different activities or transportation modes. Without good information, choices may be misdirected, and the public may be exposed to unnecessary risk.
What we need: We need some set of common denominators that can be used to characterize transportation safety in a comparable way for comparable circumstances. It should be possible to compare the risk of recreational boating, for example, to the risk of recreational flying or recreational driving. Similarly, the risk of working on a ship should be comparable (even if not equal) to the risk of working on a train, truck, bus, taxi or airplane.
Benefits: Denominators allow us to express safety in terms of risk, and comparable measures of risk allow us to determine the riskiest operating environment. That may help reveal risks we were not aware of. It may help focus effort on more serious safety threats, and it will provide useful information to the public. It will also help inform policy and resource decisions, and it may offer a better basis for justifying resource requests.