Health researchers say electric scooter injuries have surged along with their popularity. A study published Wednesday found a near-tripling in U.S. injuries over four years.Nearly 40,000 scooter-related fractures, scrapes, cuts and bruises were treated in U.S emergency rooms from 2014 through 2018. Most occurred in riders aged 18 to 34. Most of the injured weren't hospitalized. The trend follows the emergence of rental companies in cities in the U.S. and abroad that let customers rent scooters through smartphone apps and drop them off anywhere in the same city.