My guess is that old polluting vehicles are slowly dying out and being replaced with the clean burning cars we have today that just so happen to get much better gas mileage than before. Also, low sulfur diesel fuel has started to hit the market.

And oh......why do we have these factors in place today? Was it Republicans that pushed for them?......(cue Jeopardy music).....Careful now.....Bowser's got his hand on the buzzer on this one and is betting his entire winnings.

Evil Kyoto. Evil Kyoto. It's to blame of course, certainly not the fact that as we've slowly shrunk away from being an industrial giant, those other countries have picked up the slack and see environmental sanity as something that will aid their quality of life. Imagine that.

Art