-NYC has ~13,605 licensed taxicabs.
-The average annual net income for a NYC taxi (in 2015, probably a bit lower now) was $58,555.
-$58,555 * 13,605 = $796,640,775
This figure is for taxis only, in one (big) city. It leads me to think that $70 billion is not an absurd number, globally.
edit: sources: https://www.yellowcabnyctaxi.com/blog/new-york-city-taxi-rev...