These conclusions have not changed, but first some air pollution background. NY, Conn. and Mass. have already adopted CA emission standards, and EPA is tightening up federal standards. Also, older CA cars emit more than newer cars, as elsewhere, due to being built to lower pollution standards and due to the insults of age and wear.
Emissions increase with speed.
Not only are total tailpipe emissions larger than previously assumed, but the shape of the curve of emissions at different average speeds is changed. They were also tested with speed profiles developed by on-road freeway and arterial driving during various levels of congestion. The vehicles were clustered by vehicle age, type and catalyst, and tailpipe emissions measured for average freeway and arterial road speeds. The new tests show higher HC emissions than the old model. For 22 of the 26 vehicle clusters, the emissions increase dramatically at speeds above 60 mph, reflecting large increases of emissions during accelerations when the engine is under high loading.