There are several pieces of research showing that the need to change trains is a significant disincentive to their use. This applies both when using them as a feeder to the air mode and when considering them as an alternative to flying.

If you need to change mode - or even just change train - on a journey to an airport, it is a potential source of unreliability. It is (I think!) twice as likely that you will encounter a delay on a trip involving two trains than if the trip just includes one. And, of course, there's the hassle of (potentially) having to change platforms and ensuring that you are on the right platform and the right train.

Again, the more modes or trains you have to catch, the greater is the probability that you will catch the wrong one!

The two factors are clearly a significant disincentive.

The need to change trains is also a disincentive to completely changing mode. Research in Austria some 10 years ago, where respondents were given the services of an individual trip adviser for guidance on rail options, showed that 57% of air travellers were only willing to use rail if certain conditions were met - and the top one was no interchange.

However, providing more through trains probably means providing fewer trains. It is not certain that passengers realise that trade-off! And I am working on a blog about travelling from Hong Kong Airport to Shenzhen where I had to catch a bus and then four separate trains - and my total wait time was very small indeed!

The Austrian research concerned journeys of less than 500 km. It was, of course, before the major security enhancements following 9/11. Would the results be the same today?

True, changing trains can still be a pain - especially in those countries where train operators are reluctant to say which platform a specific train is likely to arrive at or leave from.

But so can flying. Do security restrictions today pose as much of a barrier to air travel as changing trains does to rail travel?

Because if so, it means more and more 400 km journeys are likely to be made by road.

This needs to improve - ideas on how this can be done are welcome!