Transportation emissions are a tough nut to crack

Using carbon pricing to cut transportation emissions could be tough, and some Energy Department data from this week helps to explain why.

Driving the news: The latest entry from the Vehicle Technologies Office's handy "transportation fact of the week" series compares a decade of changes in U.S. gasoline prices to vehicle miles traveled.

The big picture: The chart above nicely illustrates something that climate advocates and analysts already know: Big fuel price swings don't change driving levels much.

• There's a number of reasons, including the fact that lots of driving isn't particularly optional and that people lack reliable alternatives in many areas.
• But transportation is the largest source of U.S. greenhouse gas emissions, so cutting pollution from the sector via cleaner cars, efficiency and mass transit is a priority.

Quick take: The data suggests that a carbon tax would have to be really high to put a big dent in vehicle miles traveled. Plus, high carbon prices — for that matter any carbon prices — are politically a tough sell.

What they're saying: "It’s just really difficult to move the needle on emissions in the transportation sector," Noah Kaufman, an economist with a Columbia University energy think tank, said.

• "Consumers may be a lot more responsive to CO2 prices than typical gasoline price changes, but even so, the impact on vehicle emissions of a double-digit CO2 price will be small, at least in the near-term," Kaufman said.

But, but, but: Kaufman, a carbon tax supporter who analyzes various Capitol Hill proposals, says they can still be a useful part of the transportation policy toolkit.

• An analysis he penned last year argued "the effect of a carbon tax on vehicle emissions may be more substantial than conventional wisdom suggests."
• He points out that in the few places with robust taxes on vehicle emissions, like British Columbia, "an emerging body of evidence suggests that the behavior of drivers has shifted far more than expected."
• Reasons why, he notes, are: policy changes are more permanent than fuel price swings; they're often well publicized and involve "shocks" rather than gradual changes.

The bottom line: Decarbonizing transportation will take a basket of approaches, as his analysis notes.

Go deeper:

• Why cutting carbon emissions from transportation is so difficult
• Automakers caught in political crossfire over tailpipe emissions
• Why automakers splintered over Trump's emissions war with California