As Krieger recounts, Japan's women-only trains came into inception in 1912 to eliminate the dishonor caused by ogling men. This type of transportation has remained in favor, as concerns of mass transit groping have persisted over the years. However it's unclear how effective the segregation is in reducing groping incidents.
According to Krieger, "Even if the number of incidents goes down, with an uptick in women reporting them, the numbers could hold steady or even rise. This might explain why the number of annual groping arrests hasn't changed a whole lot since the trains were rolled out (around 4,000 cases per year nationwide, with roughly half in Tokyo, Japan's groping Mecca, where a survey found two-thirds of young women have been harassed on trains)."
Krieger notes that a change towards good behavior could better address these problems. "It looks like until Japanese men and women – but especially men – learn to behave themselves on trains in mixed company, completely gender-segregated cars might sadly be the safest way to ride."