We’ll get a boost, but only a small one.

To understand why, we first have to understand why gas prices are falling.

Reason 1: Gas prices always fall in the winter, because people drive less. In the 27 years for which we have data, prices have fallen an average of 1% in both October and November, and another 2% in December.

Source: U.S. Dept. of Energy

Reason 2: The dollar has been gaining versus our trading partners, and OPEC spends our dollars as euros.

It takes about six weeks for oil to get from the ground to your car. As of six weeks ago, the dollar had gained 8% vs the euro, and oil prices had dropped 27% (to $100 a barrel). That’s the 23% savings we’re seeing now at the pump.

Since then, the dollar has gained another 6%, and oil prices have dropped another 20%. That means Thanksgiving travelers are likely to see the very welcome sight of $2.25 a gallon gas.

Reason 3: People in the U.S. and abroad are using less oil and gas. Here, mileage driven has fallen by 2% versus a year ago. That big of a reduction has happened only twice before: during the ‘73 and ‘80 oil shocks and recessions. The pattern is unmistakable. It’s happening again. As demand has fallen, so have prices.

Source: Federal Highway Administration.

Here’s the problem: The damage already done by high gas prices is too severe for us to avoid a recession. The hundreds of (additional) billions we’ve sent overseas are gone. Household finances will have to be repaired slowly and with wage income and jobs. As the chart below shows, recessions have followed spikes in oil prices even after prices declined.

Every little bit helps. But the positive impact created by lower gas prices will be overwhelmed if there are more layoffs.

In our weekly “Ask the Economist” feature, our resident Economist, Mike Donnelly, will be tackling your questions about the economy. If you’ve got a question — and no topic is too big or small — you’d like him to field, e-mail us at economist@pbp.com or leave your queries in the comments section.

Tags: Gas prices, Oil, OPEC, Recession, U.S. dollar