It's estimated that hosting the London games will cost the british taxpayer around 14 billion dollars. Justifying that sort of a spend on a sporting event is one of the most difficult tricks for any host to pull off. Organisers from venue cities for the next two Olympics are in London attempting to do just that. Rio will host the next summer games, and beyond a few days of escapist fun, their hope is to transform their cities transport system. Al Jazeera's Andy Richardson reports from London.