Bundled against the cold beneath a highway overpass on a busy Beijing intersection, traffic warden Zhao Delong waved his colored flag in frustration at the new silent killer stalking city streets.

• 隆冬时节的北京，在一处立交桥下繁忙的路口旁，穿得严严实实的交通协管员赵德龙（音）正徒劳无功地挥舞着手中的彩旗，试图让电动自行车这种新型马路杀手在路上行驶得规矩些。