I saw a study recently that California could increase it's overall average fuel economy by 3mpg if we would just take the cars that don't pass smog tests out of circulation. Smog testing has made this problem more accute: those who can't afford to keep their car passing smog often give up on maintenance completely (and thus registration and insurance!), so you find cars that just run like hell and pollute up a storm.
So: new anti-polution initiative: turn in your old beater and mileage records and get a big credit toward a newer cleaner car. Clean up the air by giving cars to the poor! Welfare cars!
Plus there's the issue of just plain old cars: a friend that has a (well maintained) '66 Mustang relates that the fuel system isn't sealed like it is today's cars and that it outgasses so many (unburnt) hydrocarbons that it would not pass a modern "smog test" _with the engine off_ ...
/jordan