Speaking as an actuary, it's very difficult to produce a single number than encapsulates the statistics of very rare events, such as aircraft accidents. Because they're so rare, we need to capture the statistics over a very long period (at a guess >20 years?) in order to eliminate short-term fluctuations such as the very bad run that has sadly affected aviation over the last few months. But over such a long period, the nature of flying has changed - the fleets are different, the mix of journeys are different, operations are different (2-man rather than 3-man cockpits).
In reality, the destination determines the mode of transport. Living in England, if I want to go to central London, I take the train - if I want to go to New York, I fly. The only exception I can think of is a few routes in Europe where high-speed trains offer an alternative to flying.