Effective transport - effective public transport - is fundamental to the success of the Olympic and Paralympic Games. On the peak days of the 2012 Olympics, a train will arrive in the Stratford area every 8 seconds. How do the 2016 cities size up - bearing in mind that there is not a lot of time to make fundamental changes to the public transport system?

Rail links to airports are obviously of interest to my organisation, the International Air Rail Organisation (IARO). They are also pretty important to the many visitors, athletes and hangers-on - to say nothing of the world's press - who will attend. Of the 4 leading candidate cities, Chicago and Tokyo have good rail connections to their airports. Madrid has a subway line between Barajas Airport and the office district in the north of the city: Rio de Janiero is considering rail links to its airports.

Madrid and Tokyo are served by high speed rail: Chicago and Rio are not.

Chicago has 11 suburban railway lines with a route length of 798 km: the network has 280 stations and O'Hare airport is served (although not very well). The downside is that some of these lines are "commuter rail" rather than "suburban rail" - they have services inbound in the morning and outbound in the evening and very little in between or after the peaks. No doubt for the Olympic fortnight these could be supplemented.

The city has 7 subway lines extending to 168 km, with 144 stations: both airports are reliably served 24 hours a day.

There is also an ambitious plan to connect both airports to the city and each other by airport express. Under the stimulus of the Olympics, this could well happen. IARO has been involved in the discussions behind this imaginative plan. If it did happen, that really would be a valuable legacy of the Games!

Madrid's suburban network has 9 lines (339 km of route, 118 stations).

An airport connection is planned, for both suburban and high speed trains, supplementing the present subway line connection. Given Spain's recent railway development history, these are highly likely to be in place by 2016.

The metro system has 12 lines, 282 route km and 231 stations. One line connects the government office area with the airport: there are connections from this line to some of the other subway lines.

Rio de Janeiro has a complex 264 km suburban network with 127 stations: an airport connection is planned.

Its 2-line 35 km subway has 32 stations.

Tokyo's extensive suburban network has 60 lines, 2900 route km and 1200 stations: both airports are served.

Its 4 line subway has 281 route km and 282 stations.

If the decision was to be solely on transportation grounds, Tokyo has to be the clear winner.
Madrid probably scores better than Chicago. Its suburban rail system has a better service than Chicago's, which runs on lines shared with intensive heavy freight traffic. Madrid's subway system is also more comprehensive, although less spectacular than Chicago's famous "El"!
Rio, with smaller networks, has to score low.

Rail is best for coping with high volumes of traffic - trains carrying 1300 seated passengers can run every 2 minutes each way on a 2-track railway.

This kind of capacity is necessary for Olympic crowds.

Olympic-driven improvements to the rail network leave a valuable legacy, as we are starting to see in London. The infrastructure can be used for 40 years: rolling stock, while not infinitely "go-anywhere", can certainly be used after the event in a wide range of places. Improved signalling can provide extra capacity for commuters way into the future, and enhanced ticketing and information systems will be useful for the rest of their lifetime.

Many visitors will not have cars available: buses and coaches are valuable but have a lower capacity than rail. They are useful for serving more dispersed areas, but not for the intensive flows to the main centres.

The city which wins will need to gear up very quickly. Capacity improvements will need to be planned into a dense urban fabric - not an easy task. There is a lot of valuable experience available from past Olympic cities - and of course from London. It will be almost essential for the winner to draw on this to ensure success.

There are two absolute certainties. The event cannot be postponed, and the eyes of the world will be on that city during the Games.