Turning car engines off while waiting at traffic lights, as recommended by Japan's Environment Agency as a way of cutting carbon dioxide emissions, can cause congestion and consequently even greater pollution, according to the results of a test conducted by the National Research Institute of Police Science released Friday. The agency recommends switching off car engines, rather than leaving them idling, as a way of preventing global warming. But officials at the institute said that if cars stop for less than one minute, switching engines off will only lead to greater carbon dioxide emissions.