Now, here's the reason: the price of oil (a key component of gasoline) has not dropped, despite ample global oil supplies. For a variety of reasons (asset play, inflation fears, weak dollar hedge) the price has essentially doubled in the past year, pushing the average price of unleaded regular to $2.65 per gallon in the U.S. High-cost metro areas, such as New York, Los Angeles, San Francisco, and Boston, are already experiencing prices over $3 for super unleaded.

Now, factor-in what will happen to gas prices when demand starts to pick-up in the U.S. Assuming flat oil prices, an average unleaded price of $3 seems like a done-deal, followed by a quick run to $3.25 in the spring. However, if oil continues to rise toward $100 per barrel, an average price of $3.50-$3.75 would likely occur.

The key to gasoline's impact on U.S. economic performance moving forward will be how long gasoline prices remain at elevated levels. To be sure, if they remain at $3.50-3.75 per gallon, GDP growth will certainly take hit. It's also hard to see how the U.S. economy could grow at an adequate rate amid $3.50 gasoline: already pinched disposable incomes will take another hit, taking another bite out of commercial activity. Every $1 per barrel rise in oil decreases U.S. GDP by $100 billion per year and every 1 cent increase in gasoline decreases U.S. consumer disposable income by $600 million per year.

Further, the 2008 summer spike in gasoline prices to over $4 per gallon is not the best case study because the price soon collapsed as the leveraging bubble ended. Can the U.S. economy hum along in face of $3.50-3.75 gasoline? In theory, if Americans conserve -- and suddenly purchase millions of fuel-efficient vehicles -- is it possible, but the calculation here is that, at minimum, GDP growth would slow substantially, and a double-dip recession could occur.

So to get a quick-read regarding where the U.S. economy is headed, just look at the price at the gas pump.