Air Quality in urban areas has improved because the emissions from motor vehicles have been greatly reduced over the years. Testing had NOTHING to do with this. The original purpose of emissions testing was to reduce the amount of Carbon Monoxide which was approaching lethal levels in many urban areas. Those days of “Test Pipes” and carburetors with open idle mixture screws are LONG past…Todays cars, and to a lesser extent, trucks, speaking of the entire fleet, are squeaky clean compared to the “fleet” that existed when emissions testing was imposed on motorists. Failing 3 or 4 percent of today’s fleet because the EGR valve supposedly has low flow or some other computer code makes absolutely no difference in air quality…That big cement mixer that belches black smoke and NOx from a pair of 6" diameter pipes produces a thousand times more air pollution than the worst “Gross Polluting” passenger car… No emissions test for him…