The effects of living near main streets were weaker in 2002 than in 1991, which may have been due to stricter requirements on auto emissions, the researchers note.

• 研究人员发现,与1991年相比,2002年靠近主要道路居住的影响减弱了,这可能是由于对汽车尾气排放有了更加严格的要求。