Gallagher, the comedian best known for the “Sledge-O-Matic,” noted that people must like crowds because wherever you see a crowd, you see a lot of people. This observation is not altogether facetious when describing air travelers. Every day hundreds of thousands of flyers seem to prefer to deal with the crowds associated with air travel—perhaps “endure the crowds” is a better description—rather than make use of other, roomier, but slower forms of transportation.

The presence of other travelers in close proximity to us, repeatedly invading our personal space, does however, take its toll in increasing our levels of stress. But why does the nearness of strangers make us anxious? And what can we do to avoid that anxiety when traveling?

Each one of us has our own “personal space,” an invisible area around our body that, when penetrated by others, makes us feel uncomfortable, sometimes even afraid. The boundaries around our personal space expand or contract depending on, for the most part, the relationships we have with the people who approach us.

For strangers, that boundary is set at about a foot and a half, but this distance changes too. For instance, all other things being equal—which of course is rarely the case when considering human interaction—pairs of men keep greater distances from each other than pairs of women. And male/female pairs get the closest—unless the interaction is threatening, in which case women allow the most space. (Interestingly, the popular notion that a person’s cultural background affects the boundaries of his personal space has not been convincingly borne out by research.)

How does the concept of personal space help us understand why we feel anxious when traveling? Dr. Jonathan Bricker, Staff Scientist in the Department of Psychology at the University of Washington studies the behavior of air travelers and the causes of their stress. Bricker has found, not surprisingly, that standing in line at airports—being crammed cheek-to-jowl with others—is one of the biggest stressors in air travel today. And that stress is hardly alleviated when passengers find themselves in crowed departure areas or sitting on airplanes packed to capacity.

“The constant crowding that happens to travelers can make them feel trapped,” says Bricker, “and the response to that entrapment is fear.”

So what can you do to defend the boundaries of your personal space against intrusion and thereby reduce the stress of travel? Here are a few tips if you don’t want others invading your space.

Maximize the number of vacant seats between you and others.

Select a seat that is not immediately on a pedestrian throughway.

Choose what environmental psychologists call “sociofugal seating.” These are arrangements of chairs that discourage social interaction. Seats that are in straight lines, that do not closely face one another, or even better, that are positioned back-to-back are examples of sociofugal seating.

Keep your face buried in activities like reading or paper work, hunch over your task, appear preoccupied, look down, and for sure don’t make eye contact.

Set up physical barriers. For example hold a newspaper up in front of you and place personal items on adjoining chairs. Erect psychological barriers by “tying” yourself to another object or person. For instance, watching a television can prevent people from positioning themselves between you and the monitor; striking up a conversation with a person one seat away can discourage people from sitting between the two of you.

Finally, spend more on your transportation and lodging. As Dr. Bricker notes, “Much of what is purchased in ‘luxury’ travel is personal space.”

If none of these techniques work, remind yourself that most of the people who are intruding into your personal space are having their personal spaces invaded by you. There is some sense of comfort knowing you are all in the same boat… or airplane.