City planners around the globe are increasingly touting the merits of public transit systems as a preferable transportation alternative to roadways and private automobiles in high-density urban environments.

With public transportation set to play a role of increasing prominence in resolving the congestion and pollution problems of the world’s major cities, it’s important to give full consideration the options at hand that could eventually emerge as the mainstream transit solutions of the future. London’s Heathrow Airport has already…