Motor-vehicle-pollutants portion rising?, falling?, what?!

Alan Kandel asks at Science Blog: Motor-vehicle-pollutants portion rising?, falling?, what?!

Consult most news sources these days – this one included – when it comes to poor air quality, and what you’re likely to uncover is that more often than not in the blame-game, traffic – more specifically, tailpipe emissions – is named. Obviously, not the only source of pollutants, nevertheless, the portion of pollutants coming from traffic – and transportation, more universally – is sizable.

Falling gasoline prices: What effect is this having on both motor vehicle and public transit use and, by extension, what, if any, impact has the decline had and having on the quality of our air.

He cites my earlier post

David Levinson in “Mount Transit, Mount Auto, Mount Next,” at the Transportationist Blog, clues us in.

“In the US, we have seen a great struggle play out in the twentieth century between what David Jones calls Mass Motorization and Mass Transit. The conflict between the modes continues to this day, and has become a morality play in the culture wars. While they mostly serve different markets, they compete for users, and roadspace, and funding, and the hearts and minds of travelers. They are competing on old turf though, …, both modes appear to be in decline, transit for decades, the decline of the auto-highway-system is just beginning.”

This is an interesting revelation, because what this tells me is pollution from both sources should be becoming less and less, that is, as long as the mode-split-relationship (and other influencing factors) has not significantly varied.

He doesn’t outright state a final conclusion to the question, though he says:

But, then I noticed something interesting. The overall trend was positive between 1961 and 2007, taxed gallons going from 60.006 billion in 1961 to 177.394 billion in 2007. After the Great Recession hit just subsequent to this, the number of gallons of gasoline taxed dropped to 171.229 billion in 2008, dropping even more to 168.551 billion in 2009, rose again in 2010 to 171.101 billion, falling to 168.722 billion in 2011. Only if there are fewer less-fuel-efficient vehicles on the road coupled with greater use of cleaner-burning fuels and/or less traffic on the roads coupled with greater use of cleaner-burning fuels – along with the dip in the amount of gallons of gasoline taxed, am I able to conclude that emissions emanating from motor vehicles are also fewer. That’s a good sign even if the number of motor vehicles on America’s roadways experiences level or upward growth.