India, March 28 -- In Naples, Dante and two active volcanoes form the inspiration for a subway stop designed by Anish Kapoor.

In Paris, an inverted skyscraper lets playful natural light dance all the way down to platforms 50 metres below the surface.

In China, a spiral Shenzhen Eye crafted in glass and steel signals the aspirations of a booming business district.

So why the dramatic designs now? According to the Belgium-based research non-profit International Association of Public Transport, there are currently such networks in 202 cities across 63 countries, up from 101 cities in 2001 and under 50 cities in the 1980s. Sub-Saharan Africa just got its first, with a major, high-capacity link opening in the Cote d'Ivoire last year.

As ne...