If you thought about it, which U.S. states would have the highest percentage of total income spent on driving? 

We'd have guessed Alaska, Montana, New York and Hawaii would rank in the top 10.

But no. Guess who is No. 5?

Idaho is the No. 5 state in terms of percentage of income spent on driving, according to a recent survey by the National Resources Defense Council for 2010.

The council's recently published "Fighting Oil Addiction" report (PDF) evaluates all 50 states with regard to their vulnerability to changes in gas prices. Idaho is up there, but none of our other guesses are.

Montana, however, is No. 11. Washington is No. 45.

The data collected in the survey say this:  Idaho drivers spend roughly 5.8 percent of their total income on driving. Washingtonians spend 3.6 percent. Click on the chart below to get a slightly larger summary of those numbers.

Not clear is whether the numbers are measuring all state residents or only its drivers. We'll have to check that number.

The map above shows the states most vulnerable are those with relatively low incomes and less dense populations. Mississippi, South Carolina, and Kentucky have the sorry distinction of being the most vulnerable.

Idaho, Montana, Nevada and Utah form a pocket of higher vulnerability across the West.  Drivers in those states, one can argue, really drive longer distances on average, which will boost their spending on fuel.

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