The day before Thanksgiving brings its own tradition, this one will be revisited on American roads Wednesday.
"Every town has its worst traffic corridors and worst bottlenecks, and those roads on Wednesday afternoon — because you have a combination of travelers and commuters — will have their share of pain," said Jim Bak, director of community relations with INRIX, a company that provides real-time and predictive traffic information.
Here's the typical day-before-Thanksgiving scenario: The morning commute is relatively mild but, across the nation, afternoon traffic picks up about an hour earlier than usual and congestion doubles, compared with a regular Wednesday afternoon, Bak said.
In general, the end of the year brings not only holidays but increased travel times, and INRIX data show these usually climb in November and December, he said.
For drivers heading across town or across country, this can lead to a familiar phenomenon, according to Dwight Hennessy, a traffic psychologist and associate professor at Buffalo State College in New York.
"You've got more people out than the roads are designed to handle, and what does that lead to? Congestion," Hennessy said. "It makes it seem — and it is all perceptual — that traffic is weighing down on me. People are doing things l don't like, and it becomes more stressful." [The Science of Traffic Jams]
The bad news is that sometimes we aggravate the situation ourselves. The good news is there are ways to cope.
Traditions on the road
The "early leaver" phenomenon, when travelers and commuters hit the roads earlier in the afternoon and in greater numbers, isn't unique to the day before Thanksgiving, it's also a given on the Fridays before Memorial Day and Labor Day (which are always observed on a Monday), according to Bak.
Traffic patterns, and ensuing traffic jams, aren't as predictable around Christmas because the holiday falls on a different day of the week each year and drivers' travel plans vary, he said.
Typically, around the country, travel times go up about 20 percent the Wednesday afternoon before Thanksgiving, as opposed to the roughly 10-percent-to-12-percent increase typical for a regular Wednesday afternoon rush hour as compared with the average for the day, Bak said.
In other words: If, on clear roads, your journey ordinarily would take you 60 minutes, you should plan on 72 minutes on Wednesday. Certain crossroad cities, such as Hartford, Conn.; Atlanta, Ga.; Baltimore, Md.; and Chicago, Ill., can see the biggest increases because many travelers pass through them on their way to other destinations, Bak said.
This isn't true for the rest of the holiday weekend, with people's return plans being dissimilar enough in general that there is no significant spike on, say, Sunday afternoon, he said.
Conditions vary from year to year, with the state of the economy playing a significant role: In lean years, the roads are less crowded than during boom ones.
This year, the American Automobile Association (AAA) projects that 42.5 million Americans plan to travel 50 miles or more from home during the Thanksgiving holiday weekend. Ninety percent of them plan to drive to their destinations.
While AAA says this represents four percent increase in holiday travelers on the roads over last year, INRIX projects a decline this year, thanks to a less rosy economic climate. The discrepancy is mostly due to differences in how both organizations arrive at their projections, according to Bak. Both, however, expect to see more travelers using buses, rails and other alternatives to planes and cars, as well as taking trips that are closer to home.
In your head
Congested roads don't create stress, our minds do, according to Hennessy.
"Stress is not a thing unto itself, it is an evaluation of circumstances as being overly taxing or demanding or challenging," Hennessy said.
For instance, some people love the hustle and bustle of a crowded mall, but most of us have so many other things going on in addition to shopping that we interpret the additional people in a different, and typically negative, way. When we begin to perceive those people as stumbling blocks to our goal, or as can be the case on crowded streets, as dangers, we become upset, adding to our pre-existing holiday stress levels, according to him.
Time urgency — or realizing that the trip you thought would take 20 minutes is, instead, heading toward 45 minutes — is one of the main predictors of stress, he said.
"Most people don't give themselves enough time, and because people in that situation are so aroused by time urgency, they don't think clearly," he said. In this state, we rely on our base, gut-level behavior so, for instance, when put under more stress, a person who is a yeller will fall back on yelling, he said.
While some sense of control is important for many drivers, in heavy congestion the majority of us can suspend our need for it. However, that's not the case for everyone, and some people behave in unproductive ways, such as honking, or even dangerous ones, such as weaving in and out of lanes, to regain their sense of control, according to Hennessy.
Survive the drive
So how best to get over the river and through the woods if you must drive this Thanksgiving?
- Plan around the late-day rush: "I always tell people, if you have to leave on Wednesday and you are driving, leave in the morning hours, or leave late," Bak said. "If you are traveling locally, go Thursday morning, because there is nobody on the road on Thursday morning."
- Take advantage of technology: "There are a lot of great tools out there to help you see what is going on and get better information, and you don't necessarily have to have a $2,000 navigation system," Bak said. These can provide traffic forecasts and alerts on accidents or other issues. (In the interest of full disclosure, Bak's employer, INRIX, produces just such a traffic app for smartphones.)
- But use it wisely: Hennessey advises drivers to know their routes; reliance on GPS can create problems, particularly if drivers are taking alternative routes.
- Be realistic: "Why can't we figure this out? Give yourself more time," Hennessy said.
- Don't make it personal: "Other people are going to do stupid things on the road, get ready for it," Hennessy said. But instead of thinking of that other driver as an idiot and carrying that anger around with you, try to forgive others' transgressions, he said.
- Use alternate routes wisely: Taking alternate routes can allow some drivers to regain a sense of control, but this strategy can backfire and create more stress if they too are clogged or don't connect as a driver expects. "I can only imagine how stressful it is to be lost in a place you don't know," Hennessy said.
You can follow senior writer Wynne Parry on Twitter. Follow LiveScience for the latest in science news and discoveries on Twitter and on .