http://www.epa.gov/otaq/consumer/f99017.pdf
First NOX reg was 3.1 grams per mile, currently .07 grams per mile and going lower.
I turned 13 in 1963, the year of the first emission control, positive crankcase ventilation.
Leaded gas, engines that were very tired at 100k miles, wheel cylinders blowing at 20k miles, manual drum brakes, bad accelerator pumps that could get you killed trying to get across the road, 55,000 deaths a year on US highways, windshields that decapitated you.
Current NOX regs are 1/44th the amount of the original 1970 regs.
Read the linked history to see what had to be done to reduce emissions and how much the oil and car companies fought against regulations.
Triple the oil change intervals, engines lasting 3 or more times as many miles, close to 20,000 fewer deaths per year in the US.
From the perspective of working in the repair industry for 30 years and remembering how much a single antique car STINKS just following it down the road today.
Even someone who is as critical of govt as myself realizes how much has changed, when I look out at the sunset from my front porch and I can still remember the brown haze in the 60s, 70, and 80s.
I can also remember the last days of carburetors, vacuum hose nightmares, driveability nightmares. Christ, you could not even get a brand new car to move under it's own power until you let it run for at least 3 minutes or it would stall and die, in 1973.
regards
Mech