The Psychology of Driving

Nadine Lee: You're listening to Mobility in Motion, a podcast produced by Dallas Area Rapid Transit. I'm your host, Nadine Lee, President and CEO of DART.

Nadine Lee: According to the Centers for Disease Control and Prevention, the U.S. has more motor vehicle deaths than any other high income country: three times higher than Canada, Australia, and France; four times higher than Germany and Japan; and five times higher than Switzerland and Britain.

And while most of these countries' traffic death rates are going down, the statistics in the U.S. are going up.

There are a lot of different theories on why this is happening, and what to do about it. And today we are talking to Dr. Patricia Tice, who is looking at this issue from the lens of human psychology.

Dr. Patricia Tice: My name is Dr. Patricia Tice, and I have been a transportation engineer and a planner and a researcher for about 30 years now.

Nadine Lee: According to Dr. Tice, the old way, lowering the speed limit, is not working.

Dr. Patricia Tice: The standard approach is we think that if we stick a cop out there and we change the sign, everybody's going to do exactly what the sign tells them to do.

Statistically, that's not very effective. There is a statistical impact. And it is really consistent. We know the effect is real. It absolutely is. It's just not big.

So for every 10 miles an hour difference in a posted speed limit, you get about a two mile an hour difference in the actual speed of flow. So lowering the speed limit, just with the sign doesn't seem to work very well.

Nadine Lee: And we know that people driving at faster speeds cause more crashes and more serious injuries and fatalities during crashes. So are there other ways we can get people to slow down that might work better than posting signs?

This is something Dr. Tice has spent a lot of time thinking about.

Dr. Patricia Tice: Just the last decade or so, I've been playing with ideas that have to do with urban space and the way that connection and human connection interplays with the way that we drive: A human being present.

Nadine Lee: Using data from U.S. government research called the Naturalistic Driving Study, which fitted cameras, sensors, and GPS devices on the cars of more than 3,000 regular people, Patricia and her team analyzed how we actually drive under a wide range of conditions: traffic, weather, road types, and more.

Patricia Tice: They put about a hundred instruments on each vehicle and then let people drive them for a year. And after about three weeks, you forget that you're being watched. And so we had real data from real people driving without any interventions. Just what does it look like to drive on an everyday basis?

And we pulled a very small piece of that data, very small. But we began looking at the difference between the way the environment impacted the people who were driving. And my goal when we started was to figure out how to make people behave.

Nadine Lee: Combing through this research, Dr. Tice came up with a surprisingly simple formula for predicting how fast humans will drive based on three criteria, and none of them had anything to do with speed limits.

Patricia Tice: The first of the factors was something we call doorway density.

We counted the number of doorways on a block, and then we counted the length of the block in hundreds of feet, and divided the number of doorways by the length of the block, So it's basically the number of doorways per every hundred feet. And that becomes a really simple way to measure how active the actual street you're sitting on is.

When you're driving in a city street where you're interacting with another person eye to eye, spirit to spirit, if you offend that person, there's always a risk they're going to pull out a gun. It's not a big risk, but it is a risk. But the bigger risk is that they're going to think you're an asshole.

And nobody wants to be seen that way.

Nadine Lee: We've all had that feeling when we're driving, right? You just don't see someone about to cross the street. You almost hit them. And you look them in the eye and feel like such a jerk.

That's a feeling we all want to avoid.

Dr. Patricia Tice: For the most part, we still care what other people think about us. An urban place is somewhere where you're negotiating all of your conflicts face to face, eye to eye.

When you're in a suburban environment, you've got a very large machine that you're operating and everyone else has an equally large machine. That's relatively easy to see because it's big.

And you are just moving around like you're in a video game, interacting machine to machine. And you treat the other machines around you like an inanimate object. And so you'll scream at it. You'll cuss at it.

And so when you start going into an urban environment where you're interacting face to face with other people, that social standing begins to come into play. And you begin to worry subconsciously about how other people see you.

When we look through the data, the biggest thing that we saw over and over and over again is that the features in the environment that changed the way that people paid attention, changed the speed that they went, changed the way that their vehicle moved around in the space, all of those things had to do with whether or not there was a human being present.

Nadine Lee: So the first variable is doorway density, which is actually another way of saying how many humans are on this street.

Dr. Patricia Tice: The second of the variables was the corridor width.

So the corridor width is the tunnel that the driver sees in front of him that he has to drive through. So, usually, there are barriers on both sides of the driver, and those are not the lines that are painted on the roadway. Those are things like utility poles, and on-street parking, and mailboxes, and people wandering around, you know, all of the flotsam and jetsam that are part and parcel of the street.

You're driving your car in a tunnel that's made up of all of this “stuff of life.” And so when you start looking around you, and you see this line of the “stuff of life” that runs on both sides of you, the width of that line is really what you care about as a driver. Unfortunately, it's a really difficult thing for an engineer to measure.

Nadine Lee: For those of us that drive, we know that when the road is wider, it kind of feels more comfortable to go faster. But if all those things that Dr. Tice described are closer, we experience something called optical narrowing.

This feeling of narrowing slows us down.

Patricia Tice: There's three pieces to the optical narrowing puzzle., One of the pieces is parallax and parallax is the kind of thing where when you're driving down an open road, the mountain goes by a lot slower than the tree that's next to you. Okay.

And so you get a better sense of how fast you're going based on how close the things are to you. And if you got a bunch of things that are really close, it can feel an awful lot faster.

The other issue though, that is far more important, is this issue of how far you're actually looking in the roadway for people. And when you're looking for people you're really looking only at an area about 60 feet wide. Anything bigger than that and it's out of your range for caring.

And when I say caring I'm not talking about emotions or morality. It's controlled by parts of your brain that really aren't talking to the parts that do talk. And so it's this automatic: this is a problem, this is not a problem. If they're outside of this range, they're not a problem. And I might emotionally care, but I'm more likely to disregard it because the likelihood of them actually interfering with my vehicle is really low.

But the minute you have narrow and people together, then you've got a good reason to slow down because you've got the ability to actually interact socially with the people who are there in that space.

The third one was in our data. When the corridor width got above 60-feet wide—the optical narrowing tunnel that you were looking at—when that tunnel got bigger than 60-feet wide, all of the slow speeds disappeared entirely.

And it was a vertical line on the graph, I mean there's literally a straight up and down line. Once you got past 60 feet everything below 30 miles an hour disappeared.

You start losing all of those slow speeds when that corridor width gets really wide, which is kind of scary in a design sense because we've been thinking that, you know, we could do things in some of these wider corridors that will get people to slow down, and it just doesn't happen. 

Nadine Lee: So that second variable in Dr. Tice's formula is corridor width. How close that “tunnel” that we're driving through feels on either side of us.

Dr. Patricia Tice: And then of course the third variable was just interruptions.

If you only have one person to interact with in the entire length of your drive, you're going to forget that you're interacting with them. Because, they're gone. They're out of sight, out of mind.

You have to have lots of conflict points where you're going to be interacting or you have the risk of interacting with people consistently over and over again.

So if you've got a regular four-way intersection, there are 12 different points in that intersection where a car could hit another car. And if you add in the pedestrian conflict points, that adds on a whole new pile of them.

You have to have people that are popping up. that you interact with over and over again as you drive down the length of the roadway.

When you put those three factors together, we were able to get formulas that would predict with about a 60 to 70 percent accuracy what the speed of the flow would be.

When you looked and drilled down into one city we could actually get that down to 80 or 90 percent. You can actually predict how fast the roadway is going to be based on the geometry of the roadway and the characteristics of the people that normally populate that space.

Nadine Lee: That's a pretty amazing formula, and it doesn't include a posted speed limit, speed cameras, or officers enforcing the law. It just uses the perceptions of the brain while driving.

Patricia Tice: And if you grew up driving in Tampa, you're going to have a completely different relationship with the roadway than someone who's driving in Seattle. I mean in Seattle it's a very dense grid, there's an awful lot of people walking around, transit’s everywhere.

And so all of those behaviors are kind of baked in. They're expecting to see people far more often than we would in Tampa or really even in Dallas. And so a lot of the bad, the really bad behavior was more in these vehicle dominant areas because they're just not expecting to see anybody.

Nadine Lee: Now what happens if we change one of these three levers? For example, creating interruption points.

Patricia Tice: We just had a corridor that they redid here in Orlando. They've been working on this corridor for 15 years. It's got a lot of people that walk on it. It's the red light district, so there's a lot of drunk people walking on it. It's also a low income community. The grocery store is on one side of the road, the housing is on the other side of the road, and the transit stops are on both sides.

So people are crossing this six-lane highway all the time. And they were running five fatalities a year and two serious pedestrian or bicycle crashes for like a five-year period. And this is completely unacceptable. Nobody wanted this to happen. They had thrown the kitchen sink at it.

So they had changed the speed limit. They'd changed the lighting. They'd added a few extra bells and whistles here and there. They repainted the crosswalks so the crosswalks would be a lot more visible. Yay. It didn't make a dent. It didn't make any difference at all. Ultimately, what they did in this last project is that they basically put up a crosswalk at every single block.

And so, when you drive through the corridor now, it looks like this stream of crosswalks, with signals at every single crosswalk. And it's only about a mile long, so it's not like an entire highway. But it is a good solid mile that about every 450 feet or so, there's another light for someone to cross the road.

And because of that, the speeds are so much lower in that corridor. The awareness is so much lower. They threw up fences too, by the way. They put fences down the median so that you couldn't cross except where the crosswalks were. Except there are a couple of spots that still don't have crosswalks and don't have fences.

And the funny thing is, if there's no fence, people are still crossing there. You know, human nature is what it is. It's only 150 feet to the crosswalk, but they're still not using it.

But in the last six months, there have been no fatalities and there's only been two serious crashes. Both of them were at signals, not at these crosswalks. So I'm calling this a huge win.

You know, going from five fatalities a year to zero to me is just a massive win. But beyond just the crash records, the speed is so much slower. And even when people are crossing where they're not supposed to, the drivers are going so much slower, they can actually see them and avoid them.

And we're not having the same kind of crashes that we did before. And I love that. It took an awful lot to get that to work. 

Nadine Lee: So, after looking at all this research, does Dr. Tice think we need speed limits at all?

Patricia Tice: I think we actually would be significantly better off without speed limit signs in the long term.

In the short term, if we eliminated speed signs tomorrow, we'd probably have about two years of really nasty behavior. Because people would readjust in ways that would not be pleasant in the short term. I think it would settle out over the long haul that people would ultimately end up choosing speeds that were fairly consistent with each other.

The place that speed signs are often attempted to be used, and this is one of those that's sort of a chicken and egg problem: Communities will post things at 35 miles an hour to try to signal to the driver that there's more than just driving going on here. The problem that I have with that is 35 miles an hour is about the worst speed you could possibly post it at for pedestrian safety.

That's probably the speed that you're the least aware and that they're going to expect you to pay attention to them. This is where that mismatch becomes the worst. It's like a sweet spot for killing people. And I hate that, but it is realistic. You know, if you can get that speed down into the low twenties, have at it, do it.

Do whatever you can to do that. If you're not going to get it down, then you need to be very intentional about making sure that the people who are walking there know that it's not safe.

We're trying to signal to the driver that they need to be going slower, but we're not really telling them to go slow enough. And we haven't given them an environment that tells them it makes sense to go that slow. One of the ways to get out of that spiral is to start thinking about putting things between the sidewalk and the roadway.

Nadine Lee: This is the optical narrowing that is part of Dr. Tice's predictive formula about corridor width. It looks at how things like objects on the sides of a roadway can influence how people drive.

Patricia Tice: When you start adding things back in between the sidewalk and the roadway, the drivers now have skin in the game.

And it doesn't necessarily have to be as solid as a tree. We have things that are breakaway. So if you hit them, it's not going to kill you as the driver.

And if you're in the process of changing the land use, so you actually have the doorways, you have the connections that would get people there, you can begin to transition that roadway to a much slower speed naturally, organically, without having to force them to change.

They'll change that without really thinking as the people begin to repopulate the space. But it's like getting the swallows of Capistrano to return. Until you can actually get the people there, the drivers aren't going to change their behavior. Until the people feel safe enough to be there, they're not going to be there.

And if you don't give them a good set of places to go, they're not going to be there. So, you find ways to make them feel safe while you're giving them places to go. That begins to increase the people that are there. As the people increase, the speed of the traffic slows automatically.

But you have to start that spiral somewhere, and the first place to start that is between the sidewalk and the roadway.

Nadine Lee: Dr. Tice's work has changed the way we think about how drivers drive. Why they drive the way they do.

So, what is Dr. Tice like when she gets behind the wheel?

Dr. Patricia Tice: I am a terrible driver. I do this research because I am such a terrible, awful driver. I am extremely squirrel prone. I'm good at research because I'm constantly collecting a wide range of information from all around me, but that means when I'm driving, my eyes are everywhere.

So I know if I can get an environment where I automatically do the things that I'm supposed to do, then I can get everybody else to do that too. Right? And so the goal was to figure out what that is. What does a driving environment look like that people behave in?

Nadine Lee: So when I lived in Denver, I talked to a planner about how fast people were driving down Champa Street and this planner said the most interesting thing to me. She said the easiest way for a neighborhood to slow people down on their streets is to have everyone parking exactly 18 inches away from the curb. And when you think about that, if you have parking on two sides of the street and everyone parks exactly 18 inches away from the curb, you effectively narrow the street by three feet, 36 inches.

So it would have been fascinating to see what would happen if we did our own sort of guerrilla tactics and narrowed the street by three feet because we could and then see if traffic actually got slower.

I tend to think that it would.

Thank you to Dr. Patricia Tice for this fascinating view into the psychology of roadways. You can subscribe to her newsletter at profoundinsights.substack. com.

This has been Mobility in Motion. I'm your host, Nadine Lee.

We'd love to hear from you. If you'd like to share your feedback with us, please email [email protected].

This episode was produced by Neille Ilel and The Glue, edited by Jim Gates, with music by B.C. Campbell.

If you liked this episode, be sure to subscribe and tell a friend. Episodes come out every other week and are available on your favorite podcast platform.