What factor, besides propulsion technology, is described as the 'final layer' crucial for maximizing modern physical travel freedom?

Answer

The rise of the internet and sophisticated online booking systems

The final layer of modern travel freedom is described as an innovation in information management: the internet and online booking systems, which allow travelers to exploit physical means with greater efficiency.

What factor, besides propulsion technology, is described as the 'final layer' crucial for maximizing modern physical travel freedom?
inventionTraveltransportfreedom