20 Percent.Researchers surveyed households within a half-mile of a new rail line in west Los Angeles, and found increased use of public transit. But women upped their rail trips only half as much as men. And of the women who said they do not use the train, Wired magazine reports, 20 percent cited concerns about harassment or threats to their safety. The study, by researchers at Tamkang University in Taiwan, the University of Southern California, and the University of California at Irvine, underscores the importance of safety in boosting public transit use and reducing greenhouse gas emissions. Among the safeguards female riders would prefer, according to other surveys: more lighting in stations, more staff on hand, and more stops near busy commercial centers, where harassment and attacks are less likely to occur.