While those trapped inside the maddening starts-and-stops of traffic may feel otherwise, a jam-packed highway is a calm sight when viewed from above. It's a psychedelic river of two-ton metal hunks, swerving onto ramps, lining up to get off of them, and crawling all throughout the bulbs of the cloverleaf interchange. Now and then, the river speeds or slows, sometimes for concrete reasons like drastic curves, sometimes by mysterious forces which attract and repel the flow into eddies.

If we're keeping the highway/river analogy going—and why the hell wouldn't we?—watching a police car enter traffic is like plunking a log into that stream. Every driver knows of the cop's presence, almost immediately; you can tell by the parade of brake lights greeting the officer's arrival on the scene.

“It's automatic,” says Leon James, a University of Hawaii psychologist who studies driving. “A police car shows up, my first instinct is to hit the brake. Without thinking.”

The presence of police vehicles in traffic—be it highway patrol, vehicles from nearby precincts taking shortcuts across town, even citizen cars that happen to be the same make/model—affect the drivers nearby, that is without question. But what is driving these fleeting, wordless interactions?

Certain careers are associated with an emotional response. Hear someone's a doctor, and you believe them to be intelligent. Meet a street artist, and you're probably not going to immediately ask for financial advice. The career of “police officer” is fraught with more emotional baggage than nearly any other.

A police officer can be associated with positive feelings when, say, one is dealing with a horrific situation (“Hooray, the cops are here!”). A police officer can also be associated with negative feelings, especially if you're not living as a white male. What doesn't really ever happen is a completely neutral feeling when a cop is present. If you see a cop walking down the street, you mark them, at the very least to make sure you don't do something silly like jaywalk. This “keep an eye on them” mental notation we perform on the street is nearly the same as our reaction when we see a police car on the road.

“You see people fumbling around, straighten up and pay attention. Or people quickly put on a seatbelt. They try to discretely put it on, like we couldn't see it. We see those.”

“When I'm driving and see a police officer, it makes me second guess my speed limit,” says automotive expert Lauren Fix. This is easily the most common reaction. It doesn't occur because the driver is doing something wrong; it's an entirely different feeling than, say, seeing a cop after shoplifting. Rather, we could be doing everything completely right behind the wheel, but we're still going to slow down to double check.

“Most people are affected with fear, respect, and concern when they see a police car around them,” James says.

Where do these associations come from? When do we begin seeing police cars as a reminder—for most, a menacing one—to make sure everything we're doing is by the book? The obvious answer is conditioning from driver's ed class, where instructors drill our country's impressionable youngsters about statutes, laws, and financially stiff penalties for their actions. (At least, before kids were able to take driver's ed class by clicking through slides online.) However:

“Oh, way before then,” James says. “We grow up in a car culture. The car changed everything. [These feelings] are transmitted from generation to generation in the usual ways. News, books, TV, discussion, and so on.”

In other words, we act this way because that's the response we've been taught. Maybe your uncle got pulled over when you were in the back seat. Maybe your buddy's dad pointed out a cop and told you, quick, get on that seatbelt. Maybe you grew up in a neighborhood patrolled by cops who had horrific relations with the residents. We've grown up in a car culture, and part of that culture is the fact that a small percentage of it is surveilling the rest of us.

This inducement of concern/fear isn't what police have in mind when they pull onto the road. “Everything we do is just to remind drivers to drive safely, watch for other drivers, pedestrians, bicyclists,” says San Francisco Police Department Spokesman Wilson Ng. “We're not here to scare people.” But scare people, they do. It also doesn't lead to the most pleasurable drive for cops. Imagine that your car was given an extra-special superpower: to slow traffic around you to a crawl. “They slow down,” Ng says. “You see people fumbling around, straighten up and pay attention. Or people quickly put on a seatbelt. They try to discretely put it on, like we couldn't see it. We see those.”

(Back in 2013, writer Aaron Bragman created a faux police car—with official-looking decals, roof lights, and yellow stickers that said “not in service” to avoid pesky “impersonating an officer” arrests—and drove it through Detroit rush hour traffic. The slowing of traffic was most obvious when he was on side streets. “If there's nowhere for people to easily move over, their default action is to go 5 mph below the speed limit. Meaning you can't get anywhere quickly when driving on side streets and around town.”)

While it might be annoying when you're trying to get home after a particularly long and grueling shift, police officers are fine with this response. “Of course, we want them to drive like there is a police officer on the streets watching them all the time,” Ng says. “That's when they drive the best.” That mental state is also where—sorry for being a buzz-kill—the more insidious nature of police vehicles roaming the streets enters the conversation: the psychology of living in a surveillance state.

In 2013, the Guardian released a series of articles looking into how a sense of constant surveillance affects our psychology. It's not pretty: The knowledge leads to higher levels of stress, anxiety, and fatigue, promotes a sense of distrust between the public and the state, breeds conformity, and, ironically, undermines the influence of authority.

Constant surveillance leads to higher levels of stress, anxiety, and fatigue, promotes a sense of distrust between the public and the state, breeds conformity, and, ironically, undermines the influence of authority.

In fact, that we drive a little slower around cops shows how little we respect the surveillance. The drastic difference between With Cop or Without Cop is evidence of the small lasting effect it has. We're conforming, sure, but only until they're out of sight. If we thought cops were always around, we'd always drive slowly, always make sure our seat belts were on, never check our phones. But that's not the case.

“We inhibit doing what we want to do because of external surveillance punishments,” James says. “Once we think external surveillance is not present, we follow what we want to do.”

Our reaction to their presence shows how little we worry about them when they're not around, when we enjoy a spiritual return to our newborn selves, before object permanence, when peekaboo was the most exciting thing around. Not believing surveillance is constant—a difference from our lives when we're in certain situations: on the Internet, in an office building, standing in line at the bank—is what allows us, in a way, to act like ourselves (sometimes, not the prettiest sight!) when we're driving in our little protective bubbles.

The road, then—as countless country and classic rock songs have already claimed—is a place where we feel free. Except when a cop's around, or during the seventh circle of hell that is the California rush hour.

The Sociological Imagination is a regular Pacific Standard column exploring the bizarre side of the everyday encounters and behaviors that society rarely questions.