One way to predict traffic on the roads at Thanksgiving is to look at the car-to-plane travel gap:

Drivers will make up about 89.5 percent of holiday travelers this year, a gain of 0.1 percentage point from 2013, while air passengers will drop by the same amount to 7.5, forecasts prepared by Englewood, Colorado-based IHS Inc. show. A 0.1 point increase may not seem like a lot, but based on last year’s estimate that 39.6 million people traveled by car for Thanksgiving, that would roughly equate to at least another 40,000 people piling onto America’s highways.

The car-over-plane travel choice is made easier by the fact that airfares aren’t coming down like gasoline pump prices are. While the plunge in oil has driven down wholesale jet fuel prices 17 percent since August, almost matching the 18 percent drop in retail gasoline, airfares have risen 3.4 percent over that time, data compiled by industry groups show…

“Right now the airlines aren’t in the sharing mood,” Rick Seaney, chief executive officer of the Dallas-based travel website FareCompare.com, said. “They just went through six years of multi-megamergers and dividing the country up by city with little or no competition, so they’ll pocket whatever difference they may get for a while.”

Gasoline’s drop will save the average U.S. driver about $500 annually, helping boost consumer spending, according to IHS. U.S. auto sales have risen 5.5 percent to 13.7 million in the first 10 months of 2014, on pace to be the strongest in eight years, Woodcliff Lake, New Jersey-based data provider Autodata Corp. said.

A few thoughts:

1. Having 40,000 more people on the roads at Thanksgiving is going to complicate traffic all across the United States? Spread these people cross hundreds of metropolitan areas and assume they aren’t all leaving at the same time (Wednesday after work) and adding that kind of volume may not matter much at all.

2. The prediction of future traffic is interesting to me. This reminds me of Carmageddon fears, first in Los Angeles (twice) and then in Chicago earlier this year. This seems like the creation of news: get prepared for more Thanksgiving traffic now! It is the kind of fear-based reporting done by many local news outlets about things like weather or traffic, fairly mundane events that occasionally turn out to be horrible.

3. The Carmageddon cases hint at another piece of this prediction: making such claims could change future behavior. If Americans hear that there will be more drivers at Thanksgiving, even just a few of them changing their plans (not driving or changing their departure times) might go a long ways toward relieving the predicted traffic. Perhaps this forecast is all part of some plan to actually reduce Thanksgiving traffic?

4. Just from personal observation: plane tickets appear to be really high during Thanksgiving, Christmas, and New Year’s this year. As the article notes, airlines are looking to make money and haven’t budged much in their prices even with the recent gas price drops.