Smart visas, indeed, smart ticketing in general for mass transit provides a tangible way forward in addressing some of the barriers to the seamless growth of cross border visitor numbers.

Given unpredictable fuel costs in a climate-challenged world, the future for the aviation industry must surely lie with greater efficiencies in the short term and with alternative fuels used in the future, even if a global emissions trading mechanism is put in place. The railways are likely to be the mid- to long-term solution for mass domestic transit, particularly linking to intercontinental airport hubs for leisure, work and shopping, especially in those countries with modern railway networks, such as China, Japan and the Middle East, but also across the high-speed networks of Europe.

Regarding World Heritage Sites already at risk from the sheer numbers of visitors, it has been suggested that charging a tourist levy for entry is one solution to limit the numbers, though critics have said this is elitist.