Science Friday
Hosted by Flora Lichtman and Ira Flatow
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Are traffic engineering decisions based on evidence-based research? Not as much as you might think.
4,125 words · 7 speakers
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This is Science Friday. I'm Flora Lixman. Today in the podcast, are we in the dark ages of traffic engineering?
Where people are actually dying or having severe injuries, those tend to be the roads that have most of our engineering science put into them.
When you see a car crash on the road, you might wonder, which driver was at fault? But what if that's not the right way to think about it? What if that crash could have been avoided entirely if the roads were designed better? Designed with more updated science and data in mind? That's the thesis of my next guest, Dr. Wes Marshall, a professor of civil engineering at the University of Colorado Denver. He's a traffic engineer who wrote a book called Killed by a Traffic Engineer, which digs into the standards that have dictated traffic design for decades to find out exactly how much science they're based on. Spoiler alert, it's a lot less than you'd think, or probably want. Dr. Marshall, welcome to Science Friday.
Hi, Flora. Thanks for having me.
Okay, you go really hard in this book. Like, you're quite critical of your own field. The driving gloves come off. Why did you feel compelled to write it?
Um, anger, maybe a little bit. No, I mean, no, I mean, really, I've been doing research, I mean, for decades. And I feel like a lot of that stuff is good, but it's sort of chipping away at the tip of the iceberg. So what I was learning, I mean, the deep right dug is that foundation was really where the problems were. So it needed to be something bigger. And I'm also not really one to pull punches on this kind of stuff. So, I mean, maybe that's a little bit of my personality, but that's where I ended up going.
Okay, so I mean, you're a researcher, but you've also worked as a transportation engineer. Is there a major misconception that you're hoping to clear up for people about road design?
Well, I mean, it was a misconception like for me, too, as a young engineer. I mean, you take a couple of transportation engineering classes, you get into the workforce and they drop, you know, a half dozen of these thousand page manuals on your desk. And you assume that whoever wrote these like knows more than you did. You assume that they did their homework. You assume that there's a hundred years of science and more than that, safety science steeped into these documents. And, you know, what I'm trying to show is it's not quite so. So I'm going down these different rabbit holes to try to find the origin story. Not just pointing out what we do is wrong and where, but why we do what we do. And oftentimes it wasn't nearly what I was led to believe. It wasn't nearly as scientific as I was taught.
So, you know, for a lot of people in the general public, it's great information and understanding like how these things come together. But even for my profession, I was helping us, you know, a little bit of self-reflection and understand a little bit more about why we're doing what we're doing.
Well, give me an example of that. Is there an accepted standard in road design that isn't based in science or that's actually harmful?
Oh, there's so many. I mean, that's a fun question. Down a lot of these rabbit holes were just really interesting stories and stories that were so different. I mean, some of the basics are like, we think that we were, I mean, I was taught that wider roads are safer. And if you look at the original studies on that, that's exactly what they found. There's a study from mid 1930s, 1940s, and for decades, we cited those studies. And then we stopped citing them and we just, the idea that wider roads are safer perpetuated through time. But if you go back to those original studies, like the widest road they looked at in their first study was only 22 feet wide, curve to curve, which is smaller than any road we would put out there today. So yes, a 22 foot road was safer than a 20 or 18 foot road.
But it doesn't extrapolate to the kind of things we're building now that are, you know, 60, 80, 100, 100 plus feet wide.
Well, also I'm like Googling right now, what did cars look like in the 1930s? I mean, they're quite different. Like I imagine not just the roads are different, but the cars are different. The volume of cars must be different. Like, is that a relevant study to even invoke today?
I probably not. I mean, that's the thing. A lot of our stuff is based in theory and so much has shifted over the years. Like, we think so much will will help safety. Like, I mean, right now, there's a lot of technology being added to cars and you think it will sort of improve safety. I mean, the data would make you think that some of these technologies would almost eliminate some crashes. But then when you actually see them getting into the world, you know, it eliminates maybe a fraction of the crashes that we think it will.
Well, like specifically, like the crash avoidance tech technology, like the beeps when I'm about to hit something?
Yeah, I mean, things like that. I mean, the research on some of that stuff shows that it works well during the day and it works best if like the pedestrian in front of you or something is is light skin. It doesn't work as well at night, at dusk, at dawn, or the darker the skin of the pedestrian. So there's a lot of stuff that I guess it would be safer, especially if we do the exact same thing we always done. So like when you're changing lanes on the highway, you know, before you would use your mirrors and look over your shoulder and use the technology in addition to it. But when you start relying on just the technology, you may not get the benefits you think.
What is the ultimate goal for traffic engineers? I mean, is it to eliminate traffic? Is it to be as efficient as possible? Is it safety?
I mean, well, we always say that safety is our first priority, but I mean, honestly, it's not true. Our priorities are usually around reducing congestion or increasing capacity or increasing speed. And if you look at the way our protocols are set up, like, that's what they're leading to. It's like things along those lines, or even sometimes reducing costs. Like, safety, at best, is third. So that is part of the thing that we don't like to admit, but that's the way the system is has been set up. So if you look around most cities, where people are actually dying or having severe injuries, those tend to be the roads that have most of our engineering science put into them.
Really?
It's not, yeah, it's not the roads that were built before traffic engineers existed. Like, those ones tend to be safer today than a lot of the newer roads.
Why is that?
Um, oh, that's sort of the problem. Like, we think a lot of the stuff we're doing is steeped in the safety science, and it's not. It's really more steeped in trying to increase capacity, not even just capacity today, like capacity 20 years into the future at some distant off-peak hour, and it's not steeped in trying to help the safety of the people that live and work and play in those areas today.
Are we collecting the data we need to actually make road design better?
Oh, that's a good question, too. I mean, to some extent, yes, but not nearly enough. I mean, one of the problems I see, and it's sort of fundamental, like, we all want to have a more data-driven approach to making roads safer. And when any city, any researcher like me, when you dig into the data, all the data is telling us that we have this huge human error problem. Like, we'll be people speeding and people jaywalking. And this goes back to your original question, too. When you start looking at those actual crashes and asking why, like, why were those road users doing what they were doing? Oftentimes, you can come to a different conclusion. Like, yes, for the sake of liability and insurance and police, it's useful to sort of blame the bad actors in the system. But for engineers and transportation
planners and folks like us, if you start asking why, like, why did this person jaywalk? And you start looking at the situation we put them in, and you realize, well, the nearest crosswalk is like a half mile away. And even if they go to that crosswalk, it's not that safe of a crosswalk. And you look at the built environment between where they are and where their crosswalk is, it might be missing sidewalks or things like that. And you start to think, well, what they did in that situation was, for them, the most rational decision. Like, so from my perspective, it's us who's failed to provide a safe place to cross. And we put them in a situation where jaywalking was their best option, and then we blame them when they do so and they get killed. And it happens for almost any crash you can kind
of think of. You can start asking why, and you start getting a different perspective when you start kind of going down that rabbit hole of the why these people did what they did.
I mean, you've called it the dark ages of traffic engineering.
Well, I think someday it might be thought of that way. I mean, I, I think part of the issue too, is that we as traffic engineers, and I thought the same thing. I thought it was all steeped in all the science. And as you start looking at it, you're like, wait, what? Like, that's why we do this? And almost every time you, you get to something along those lines that it's like, oh, my gosh, like, that's the only reason? Like, that's the science behind what we're doing? Like, we need to do better. And, you know, for a lot of this stuff, I'm not saying that why the roads are necessarily safer or unsafe. I'm just saying the science we're using to tell us they are safer isn't quite what we think. And we need to have more research and more, basically empirical results to really tell us, because it might change in different contexts, too. Like, it's not as simple as we often make it seem.
We have to take a quick break, but don't go away. More on this when we come back.
If we can admit that these things are steeped in the, in the science that we think, that is really the first step to trying to move in the right direction.
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You know, we put out a call for listener questions, and of course, we got tons. Here was one that a lot of people were wondering about.
Hi, this is Joey. I have a question about traffic calming circles. So my husband's usually very even-tempered, but traffic calming circles make him growl. What problem are traffic calming circles trying to solve? And is there good evidence they actually work? Thanks.
That is a great question, Joey. So, I mean, the fundamental thing they're trying to solve is a physics problem. It's speed and our bodies can only take so much force. So when there is a crash, like the best thing you can do is like reduce the speed, like force equals mass times acceleration and reducing speed and things related to traffic calming, so not just traffic circles, but a lot of
Are we talking about roundabouts?
Sort of. I mean, roundabouts are a little bit of a distinction. These are oftentimes neighborhood traffic circles. It's a little bit of a similar to a roundabout, smaller oftentimes. Um, it's more just trying to help drivers decide to go slower through different neighborhoods. It's almost like a self enforcing type design, which, you know, oftentimes these roads, they're overdesigned. They're designed with a design speed or a factor of safety to sort of entice you to go faster than we want you. And then we put up a speed limit trying to ask you to go slower and that often is where we get the disconnect and and people speeding through these neighborhoods. So things like traffic circles can help and with the, really the best thing, a lot of those round type intersections help is it reduces
like the T-bone type crash, which is one of the most dangerous ones. Like if you have a crash in most roundabouts or traffic circles, it tends to be slower and it tends to be more of a fender bender and like for me, I'm much more focused on trying to save lives and keep people from being severely injured than trying to reduce the number of fender benders. So if we have a few more of those, it seems like a worthwhile trade off. And it especially helps in making these streets feel better for people that want to walk or bike. And it still allows people to drive too. So it kind of gives people more options and more freedom to do what they want to do.
You know, you're talking about saving lives. How big of a problem is this? I mean, how many people die from road deaths every year?
Well, we treat it as the cost of doing business, but it's not. It's huge. And in this country, United States, we're looking at over 40,000 deaths every year. Around the world, it's like 1.35 million each year. I did some math recently and I tried to figure out the total number of deaths we had in the United States, you know, since we started collecting this data in 1899. And around this time last year, we crossed the four million total deaths mark. By the end of this decade, a million of those will be pedestrians, cyclists, and within that, there's hundreds of thousands of kids that have died. So. And you look on the news every night and you can always see a story of somebody dying, but we don't sort of treat it the same way that we do like when a plane crash or a train crashes. Like those are more like a fire hose that we have to shut off.
These fatalities are treated more like a faucet dripping and we all sort of just live with it and think it is what it is, but it doesn't have to be.
How do you design to roads to make them pedestrian friendly? Are there specific things you can do other than adding crosswalks that make a road good for pedestrians?
Well, there's a lot of things you can do. I mean, I will say that where it starts is usually sidewalks. I mean, I've been in a lot of cities, like even near where I am currently in downtown Denver. I do not have to go far to find the sidewalks just will disappear. They're missing oftentimes like I have pictures of places where we built these amazing ADA curb ramps and there's a bus stop, but there's no sidewalk between them. Like, so when you look at these things, it's like, it's funny that we're so focused on technology saving the day when we can't even get the sidewalks right in so many places. But there's a lot of things we can do. It's hard to like pinpoint one, but you know, typically it's making your designs prioritize those folks to some extent because for decades they've been an afterthought.
Here's another question that a lot of people called us about.
Hi, my name is Larry. I'm in Rhode Island regarding traffic. I commute from Northern Rhode Island into Cambridge, Massachusetts, and I'm always blown away by the amount of traffic I see. What really bothers me is that I just don't understand why the slowdowns happen. And I'm expecting to see some large accident or some major incident way above that's creating all the clogging, but I don't see anything. I don't understand it. I don't get it. I don't like it. Thanks.
Any thoughts?
Yeah, I mean, that's a good question, Larry. And I will say that usually it's oftentimes not the highway, but it's, it's the pinch points when you get on and off the highway. So the. The on off ramps when you get into cities like Cambridge and like that sort of stuff happens, but it's also, you know, I live in Denver and I, I grew up in that area in Boston and, you know, as someone that didn't have to commute from Rhode Island to Cambridge, you know, I can get around without having to even be in a car. I can bike, I can take the train, but I could drive too. And getting on the highways oftentimes limits your options. So in Denver, when I had traffic in a car, it's a grid, so I can move over a street
or two. When they're on the highway, you, you can't do so. You're sort of stuck, sort of waiting for, in the kind of situation that Larry's talking about to dissipate. And oftentimes like Cambridge isn't this, but when I was commuting out to like Chelmsford, Massachusetts, and the highway was fine, but trying to get from the end of the highway to my final destination was so difficult because there was only like one option for a road. So redundancy and grids can help so much. And you can get much more traffic through a grid as opposed to one giant multi-lane road.
Hmm. Okay. Are there specific changes supported by science that should be made? Like, do we know what we need to do or do we need to do more science?
Both. I mean, to some extent, we know what we need to do. We know that we, what we put out there isn't the safest designs we could have and we can do better. At the same time, we need a lot more research to try to give us more examples. And I think the best thing you can do is look for the empirical results for where things are working, like where the streets that people love, the streets that people find charming and lovely and safe and useful or even efficient, whatever it is, like measure those streets. Let's try to learn from those empirical examples as opposed to just letting our theories guide the way. So yes, we need more research, but there is enough out there where we need to start embedding that research back into those manuals. That's one of the big problems
I found is those manuals weren't steeped in like the best research. They're steeped in our old theories.
Do you have examples of great streets? Like roads that are getting it right?
You know, it's hard because it's so context sensitive. If I point out a great street in one city, another city is like, oh, we can't possibly do that because we're not so and so. So, you know, I try to, you know, every city, and when I grew up in the Boston area, people could point the streets that they love. And if you look at the way our manuals are set up, it would be impossible to redesign those streets today because they don't fit our typical criteria or theories about what makes for good, safe designs. And that seems to be the case in most cities you go to. They have these older neighborhoods that the streets are almost illegal to build. And it's often even not times due to the manuals, sometimes due to municipal regulations, both
things like level of service. But those are the places people love, and we put ourselves in a corner where we can't redesign them. So I would say, instead of looking for, you know, some pie in the sky place from some other city in a different context or the different culture, look around your own neighborhood, city, region for places you love and see if you can replicate those.
How do we get out of the Dark Ages? What's our first step?
Admit that we're in it is probably the first step. I mean, I think that's...
That's always the first step.
Yeah. There's been some denial. I mean, there's been a few engineers that take offense with the book titled, but if they actually read it, they'll see I'm not blaming them. Like, wow, we're just doing what we were taught, and what we were taught isn't quite so. So if we can admit that these things aren't steeped in the science that we think, that is really the first step to trying to move in the right direction.
Wes, thanks so much for taking the time.
Thanks for having me. This was fun.
Dr. Wes Marshall, professor of civil engineering at the University of Colorado Denver. And if you want to read an excerpt from Killed by a Traffic Engineer, head to our website at sciencefriday.com/traffic. And that is about all we have time for. Lots of folks helped make the show happen, including...
Dave Petersman. Praise Aguchi. Kathleen Davis. Santiago Flores.
I'm Flora Lichtman. Thanks for listening.
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