Traffic stands still in Nairobi. People in Kenya's capital don't like getting into cabs driven by strangers. They prefer to call drivers they know or who their friends recommend. Goran Tomasevic/Reuters/Landov hide caption

A cyclist reacts after coming off his bike in an incident with a taxi in London in 2011. Matt Dunham/AP hide caption

It's not all pink mustaches and fist bumps in the business of on-demand car services. Jose A. Iglesias/MCT/Landov hide caption

Passenger Christina Shatzen gets into a car operated by a driver for Lyft. Virginia has sent a cease-and-desist letter to Lyft, Uber and other car-sharing services. Jeff Chiu/AP hide caption

Seattle's government has given early approval to caps on ride-share companies such as Uber. Here, Peter Faris, whose company's drivers use Uber to find customers, holds a smartphone with the ride-sharing company's app in Washington, D.C. Paul J. Richards/AFP/Getty Images hide caption

Black taxis drive down The Mall in London. A Chinese company rescued the British automaker that manufactures the famous cabs. Pierre-Philippe Marcou/AFP/Getty Images hide caption