Conventional wisdom predicts that this slow, stop and go traffic will vastly drive up emissions, choking the neighbors. But conventional wisdom is ignorant of traffic calming, confusing it with fast starts and stops on conventional collector and arterial streets, and on congested freeways where motorists are jockeying for position. And, as it turns out, conventional wisdom is ignorant of emissions in those situations too. Or perhaps because old diesel trucks and buses emit a very visible particulate cloud when accelerating. Cold starts occur at the beginning of every trip, fast or slow, whenever the vehicle has been allowed to cool down.
Diesels are, fortunately, a small fraction of the vehicle fleet, although a noisy stinky one.
Every government public information publication contains this curve. With respect to cold starts and diesel, I would further emphasize that the perception arises from our sitting in congested traffic. However, the new assays show that accelerations at low speed increase emissions of either HC or NOx much less than at high speed because the engine is under much lower loading. Still, smoothing flow with traffic calming will reduce emissions even farther. Traffic calming has been shown in practice to reduce emissions.