The number of electric vehicles on roads worldwide rose to a record high of 3.1 million in 2017, but more research, policies and incentives are needed to drive further adoption, the International Energy Agency said. The number of electric cars, including battery-electric, plug-in hybrid and fuel cell electric passenger light-duty vehicles, increased by 57 percent compared with 2016, the IEA said in a report. China accounted for 40 percent of the global total last year.