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April 26, 2022Episode 32. Beyond Skin Deep: The humble roadway is about more than asphalt and concrete.
FEATURING: Darlene Goehl
Today’s pavements bear little resemblance to the driving surfaces of the early 1900s. Research Engineer Darlene Goehl explains how decades of experimentation have led to development of the modern streets and highways that are central to our daily lives.
About Our Guest
Darlene Goehl heads TTI’s Materials and Pavements Division. She joined the Institute in November 2016 after retiring with 28 years of service from the Texas Department of Transportation (TxDOT). She earned a B.S. degree in Civil Engineer from Texas A&M University in 1988 and has been a registered professional engineer in the state of Texas since 1995. She is currently working on pavement forensic, pavement design, and seal coat studies for TxDOT.
Bernie Fette (host) (00:14):
Hello, and welcome. This is Thinking Transportation — conversations about how we get ourselves and the things we need from one place to another. I’m Bernie Fette with the Texas A&M Transportation Institute.
Bernie Fette (00:30):
Simple appearances can be deceiving. That’s certainly true regarding the surfaces that we drive upon every day. We’ve invited Darlene Goehl to join us for this conversation, to help us understand more about the humble roadway. Darlene is a research engineer at TTI, and she leads the Institute’s Pavement and Materials Division. Welcome, Darlene. Thanks for visiting with us.
Darlene Goehl (guest) (00:57):
Well, I appreciate the opportunity to talk about highway research.
Bernie Fette (01:02):
Can we start with a little history? I’m wondering if you could tell us when paved roads were first introduced in America and what they were like.
Darlene Goehl (01:12):
The first roads were very similar to the Roman roads. People are familiar with that in Europe. They’ve heard of the Roman roads; they’re still finding them. And they were just basically a gravel roadway. Large rocks. And that was brought over because that was the common practice. In the 1800s in England, they started to take those Roman roads and try to improve them the way that they were designed. So it started crushing the rock. So that was kind of brought over with the British to the United States and we started with a crushed rock and then to kind of keep the dust down, they would mix tar into the top.
Bernie Fette (01:54):
Darlene Goehl (01:54):
And so that became your first paved road, as we would see like a black top, a tar road, tarmac, you’ve heard that term. So that’s kinda where that came from because the person that created crushing the rock, his name was McAdam. So they mixed the tar into the crushed rock. They called it tarmac.
Bernie Fette (02:13):
Darlene Goehl (02:14):
And of course, a lot of people used, uh, bricks in the larger cities. Again, the goal is to get outta the mud. And so you want a hard surface, that’s all weather. So late 1800s, you know, bricks mixing the tar in the top were the most popular types of roads in the U.S. Then as the oil industry boomed, we started using asphalt and asphalt and tar are not the same thing. Tar comes from a process from coal and asphalt comes from oil. That’s the main difference between the two. And so we now use asphalt and really we don’t use tar. It was the early 1900s, really, when we started to get to more of a, what you would think of the type of paving you see now where you have black top roads and some concrete roadways.
Bernie Fette (03:06):
So if we, if we fast forward just a little bit, I was telling my friend, Cathy Reiley yesterday that I’d be having this conversation with you. And she told me, “oh, you have to ask her to talk about the non-splashing pavement!” And I’m glad that she suggested that because I think it’s a fine example of how research led to innovation in a way that’s tangibly beneficial, tangibly noticeable to people who use roadways every day. I wonder if you could explain briefly what my friend was talking about with the non-splashing pavement, and maybe also talk a little bit about what you see as the more noteworthy milestones in the evolution of roadways.
Darlene Goehl (03:48):
Ultimately, the goal of pavement is for it to be safe for you to drive on. Well, as we improve safety of the roadway, we look at the materials that we use to construct the pavement. And one of the more recent safety improvements is to remove splash and spray. So it helps you have better visibility when you drive. It helps, uh, avoid the hydroplaning problems that you may see in wet weather. The surfacing was developed. It’s actually a porous friction course is what Texas calls it. Basically, it’s large rocks stuck together with a lot of asphalt and it has voids in it so the water will flow through. Think of a popcorn ball, all stuck together, and it has air all in it. So that’s kind of what it looks like. That’s about the size of the rock. It’s about the size of pieces of popcorn and they’re stuck together.
Bernie Fette (04:39):
That is great to use an analogy like that.
Darlene Goehl (04:42):
Yeah. I have to explain lots of things to my family also, and they don’t like the technical part.
Bernie Fette (04:49):
Okay. If we step away from the one that you just described, that helps to channel the water from the roadway and thereby really improve visibility, if we step away from that one, what would say some of the other really noteworthy milestones are in pavement evolution and how research contributed to those?
Darlene Goehl (05:10):
Yeah, it, it really started in the early 1900s when we started using these, uh, newer, well, I say newer materials for the 1900s. It was newer, right? Because oil was a new thing. Cars were new. Originally we had roads for wagons pulled by horses. And as we started becoming automated using automobiles, trucks that are running on pneumatic tires, we have a different way and different amount of load that goes through the pavement structure. So to be able to support the traffic, we have to design the pavement with that in mind, and the way those forces and the loading comes from the weight of those vehicles. And so it made us look at different materials and now we have more people riding and you can imagine how rough it was to ride in a buckboard. And then you go to a car with a pneumatic tire air-filled.
Darlene Goehl (06:04):
And so you expect a much smoother ride. So from that, we need to go to something that we can pave that is smoother. We wanna control dust and other things. So we started mixing in asphalt. The Texas Highway Department started in 1917 and really took over a lot of the more local roads and was able to do a lot more influence with how we do research. Then in 1950, the Texas A&M Transportation Institute was created to support the Texas Highway Department in transportation research. The Interstate System was started in 1956. And from that there was a national road research program. They had a road test that was done from 1958 to 1960, where they built a segment of the road. They had the military come in and just drive on it continuously with loaded trucks, to look at how the loading and those trucks affected the pavement. And that’s really the basis for the pavement design procedures we have now. And before everybody just used kind of a cookbook recipe, put eight to 10 inches of crushed rock in and surface it. And now we have much more technical methods for designing pavements based on the type of vehicles that are gonna travel on that. And that all led from that road test that was created that in the 1958 to 1960 timeframe
Bernie Fette (07:33):
For lots of us, it might seem simple. Mix up the asphalt and the rocks, spread it out where you want the road to be, and then pack it down nice and flat, and you’re done. At least it looks simple on the surface. But what exactly goes into building a high-quality roadway? Why is it more precise and complicated than it might look?
Darlene Goehl (07:56):
Okay. So one of the challenges we have to build a road that other people don’t think about is we’re not building a road in a factory. We’re building our road outside. It rains. It freezes. We have traffic that we have to deal with while it’s under construction. You know, we need to keep the public moving. So there’s a lot of things that interfere with us trying to build a quality product. And unfortunately, the weather is probably one of the biggest challenges that we have to construct a good pavement structure because ultimately we wanna do is keep the water out. ‘Cause the water softens all the material, ’cause we’re using, you know, soils, natural soils, we’re using rocks that are crushed. All these things soften when they get wet. So ultimately what we wanna do to build a good road is keep water out. And if we’re building it in the rain, then it takes longer and we have to dry it.
Darlene Goehl (08:50):
And that the other thing too is challenging, I know it’s hard for the public to understand why does it take so long to build a road. Again, if I was building the road in a plant, I could work on it every day. If you actually look at how many days are available to construct, when you take out rain days, holidays, freezing days, you’re only left with about half a year you can actually physically work on the roadway. So sometimes it’s a challenge just because it looks like we take forever, but we take forever because the weather interferes with us. And one of the things that’s challenging in Texas is Texas is a huge state and different areas of the state have different materials. The eastern part of the state doesn’t have a lot of rock. It’s more river gravels and silts from the meandering rivers. So it, it doesn’t have good material as you go west, it’s more arid. You have more rocks, you get into mountainous areas and the material quality is much better. There’s less rain. So it’s actually easier to construct as you go west. And one of the things we like to do with research is you have to recognize that you have different things affecting what you do and you have to design to overcome those. And you also have to try to design to use your local materials so that you can be very cost-effective.
Bernie Fette (10:14):
So what you’re describing might also help to explain why building a road is not only more complicated than most of us think, it’s also helps to explain why it’s so expensive — why building a roadway can cost several million dollars a mile.
Darlene Goehl (10:29):
Yes. And like everything that we purchase, it’s all tied to delivery of materials, hauling fuel prices and everything to build a road has to be hauled in. And so, for example, if you’re in east Texas and you don’t have aggregate, you have to either bring that material in by rail and then haul it to the site. Or you have to truck it in from somewhere. Maybe say I-35 central Texas area going west is where most of the aggregate is at. And so you’ve gotta bring those materials in. So that’s a huge cost and the amount of material that you need to build the roadway. It’s a lot of material.
Bernie Fette (11:10):
Right. ’cause you’re talking hundreds of tons of materials.
Darlene Goehl (11:13):
Oh yes, yes.
Bernie Fette (11:15):
We’ve talked a little bit about the history and I was hoping we could shift toward the future. Can you help us understand to what extent might the emergence of self-driving cars change how we build streets and highways.
Darlene Goehl (11:33):
Now, if you look at the lane that you drive in, it’s about 12 foot wide and you can see where people drive, ’cause it tends to look a little bit blacker. You can kinda see the path. Well, if you look at that path where people normally drive, it tends to be on each tire about three foot wide. So there’s some wander when you drive just naturally within the lane, that kind of distributes the weight of that car over half the lane. So about six foot total. When you go to a self-driving car, they’re gonna drive in a path similar to a train on a track. And what happens now instead of that tire meandering over a three-foot area, it’s probably gonna be stuck in about a one-foot area. So you have a more concentrated load on the pavement within that area. And that’s gonna change a little bit in how we design that pavement to hold that loading up. It’s gonna have to be stiffer and we’re still researching that, how those effects can cause those problems with those platoon vehicles. That’s what we’re anticipating.
Bernie Fette (12:36):
And so that narrower distribution of weight that you’re talking about ends up causing more wear and tear in a more concentrated pathway?
Darlene Goehl (12:46):
Yes, sir. That’s what happens.
Bernie Fette (12:47):
Okay. And so what that means is then you may have to change the way that you build roads in the future , in part, by what you mix to make those roads, to help determine the strength or the resilience that you need?
Darlene Goehl (13:01):
Yes. And so we design now to try to have the roadway structure support the loading for 20 to 30 years.
Bernie Fette (13:08):
Darlene Goehl (13:08):
And we resurface around probably every 12 years just due to the weathering effects. The sun oxidizes and causes cracking in the top. Sometimes we’ll have to add a layer of asphalt in order to just help keep the waterproofing. Because again, the environment causes some cracking in the road. Ultimately, we need to keep water out. So we have to continue to waterproof, but those layers have a certain strength and that strength allows them to support a load that comes through the tire. And as that load is more concentrated into one spot, it looks more stress in that spot. So I’ll have to do some additional research on how you design that to continue to last the amount of time that we expect it to before we go in there and do work.
Bernie Fette (14:00):
And will you also have to consider that pavements in the future, roadways in the future, to accommodate autonomous vehicles, that those, those pavements may have to have sensors embedded?
Darlene Goehl (14:11):
Right now, the technology is working off the striping and the reflectivity in the striping. Uh, and you can see if you have a car that has some of the pilot assist and those type of things. When the line marking drops off, say you have a ramp entering or you have a turn lane starting. Sometimes the cars will pull you towards that open spot, trying to keep you in the center of the lane. And those markings have to be refreshed on a three-year cycle. So that becomes very expensive if you’re using those markings to control. And there has been talk about putting other sensors within the pavement to help guide the cars.
Bernie Fette (14:49):
Pavement research for self-driving cars is one area. But what about other major research needs that you can foresee? If you had a really big check from a research sponsor tomorrow, what’s the most pressing need that you would start with?
Darlene Goehl (15:05):
One is the material challenges we have now. We see this in every industry with the supply chain problems. And we use polymers in our pavement structures to help stiffen and work better through environmental changes through the climate change of just in a normal year. Last year, there was a polymer supply issue. And so there were some changes to those polymers. We think that’s causing some problems on the roadways leading to some early failures that we didn’t expect to see, but we need to do some research to figure out what happened, what changed, why the material still meets all the requirements yet it’s not performing. So that’s one thing is, supply chain issues still occur. We will try to, and in the manufacturers that, that we still have to continue to build the road. So they’re trying new things. The second thing that I think is important is to take the lessons that we learned from research and apply those and provide whatever training that’s needed to others who, who maybe not see our original research and are involved in the sponsorship of that research to help promote its use and to get it out there so that it can benefit all the taxpayers.
Darlene Goehl (16:19):
The state of Texas is unique in that TxDOT has on its system a lot of roadways that other states would consider to be not on the state system. All the farm-to-market, ranch-to-market type roads that are on the Texas system are not on other state systems. They’re controlled by counties and others. So because of that through the years through research and other things developed design methods for those rural roads that are not necessarily the same as the national design because national designs require bigger pavements again, because they’re made for like U.S. highways, state highways, interstate, much more traffic, much more loading. And I think there’s a huge opportunity if we had the money to take outreach and teach these things we’ve learned through research to help more rural communities apply this technology and to be able to do more cost-effective designs and get all surface roads. I know, you know, like for example, in Texas, we still have many, many counties that the county commissioner runs the road crew, right? And they’re, they’re not engineers and that’s okay. That’s what we needed. But there’s so much information out there that, you know, they’re not trained to do that. That would help them and the taxpayers of the state that for me, I, I just see that there’s an opportunity there to go out with some outreach.
Bernie Fette (17:47):
It probably wouldn’t be a stretch to say that we sometimes take reliable roads and highways for granted. If you had just half a minute to explain to the average person why having good roads is so important, what would you tell that person, maybe this would be your elevator speech?
Darlene Goehl (18:05):
The reason that good roads are important is because especially in the state of Texas, everyone travels by the roadway. Texas is a huge state. We travel several hours just to visit relatives. We have things that we buy goods and services that we use every day that are brought to us from other parts of the country, from other countries through ports and to have the roadways in good shape so that we can get the delivery of the things that we buy, that we use every day, that we feel safe to drive and visit our family or friends or take a vacation. Those things are important. And while we seem to be constructing I know the roads continuously, you know, it’s very important to keep those roads in good order, in good shape. We don’t wanna have potholes in them that could cause damage to our cars. We want a good safe road that we feel comfortable traveling on. And in order to do that, you know, we have to, uh, maintain those roads and we have to build those roads to a sufficient strength that it supports all the traffic that’s gonna travel on that roadway.
Bernie Fette (19:15):
This is something that I like to ask each one of our guests. What is it that motivates you to show up to work every day?
Darlene Goehl (19:23):
I think some, you know, something that you use every day, like the roadway, it’s very interesting to me to come in and work and feel like you’ve contributed to overall society and that improvement. And I had somebody tell me one day that we had developed a standard for a construction technique that improved safety and the person made a comment to me that you don’t realize how many lives you saved by coming up with that detail. And that made me feel really good is, you know, something that we use and we talk about safety, but safety is really important and we all drive the roads. Our family drives the roads and we want our families, our friends, ourselves, we want everyone to be safe when they drive on that. And so when you can do things to contribute, to improving the safety for everyone, that’s really worth doing.
Bernie Fette (20:22):
Darlene Goehl. Research engineer and pavement expert at TTI. Darlene, thank you for sharing your time and your knowledge with us.
Darlene Goehl (20:30):
Thanks for asking me to come on the podcast. I appreciate that.
Bernie Fette (20:37):
It’s sometimes easy to take our streets and highways for granted. They’ve become so reliable that we tend to forget how much we depend upon them for our every need. For trips as routine as a drive to work or as urgent as a response to a medical emergency. And as simple as they seem, that appearance conceals a structure that’s more complex — one requiring precision in physical science that’s built upon decades of advanced research.
Bernie Fette (21:10):
Thank you for listening. We hope you’ll be back for our next episode, and a conversation with Shawn Turner, a self-described evangelist who’s leading TTI’s emerging studies in the world of big data. Where it’s coming from and how it’s quietly but dramatically reshaping the way that we transport ourselves and everything we need. Thinking Transportation is a production of the Texas A&M Transportation Institute, a member of the Texas A&M University System. The show is edited and produced by Chris Pourteau. I’m your writer and host, Bernie Fette. Thanks again for listening. We’ll see you next time.