File photo of taxis lining up to get their tanks filled with compressed natural gas on a street in Taiyuan

 
File photo of taxis lining up to get their tanks filled with compressed natural gas on a street in Taiyuan
Taxis line up to get their tanks filled with compressed natural gas on a street in Taiyuan, Shanxi province in this December 12, 2012 file photo. REUTERS/Stringer/Files