Jane: This is But Why: a Podcast for Curious Kids. I'm Jane
Lindholm, and right now I am actually standing on an overpass
in Los Angeles, California. Maybe you can hear the traffic
behind me. I'm here in Los Angeles talking about traffic,
partly because Los Angeles is known for traffic. There are
almost 8 million cars registered in Los Angeles County, which
includes more than just the city. There are only about 10
million people who live here, so that's a lot of cars. And when
you think about all the miles that people drive around this
city and around this county every day, it's astronomical. In
fact, one of the most crowded highways in the whole world is
here, the 405 freeway. Close to 400,000 vehicles go on it every
single day, and its congestion problems are pretty legendary.
Some people call it Carmageddon, when the cars are just stopped
on the freeway. Other times people say it's called the 405,
because people can only go about four or five miles per hour. Los
Angeles has a lot of cars and a lot of drivers, and it's a good
place to start our conversation today, which is all about
traffic, but not just about lots of cars on the road. You want to
know about things like how traffic lights work, and we're
also going to tell you things like how they make highways and
traffic lights the most efficient to try to ease the
congestion that I'm seeing right now here at five o'clock on a
Friday, which is called rush hour. Hey, it's Jane back in the
studio now, it was way too loud to do the whole episode there.
And actually that was like seven years ago that I recorded that
while I was visiting Los Angeles, where I used to live.
We've been wanting to make an episode about traffic and roads
and traffic lights for a long time, even before I went and
recorded that. And today, finally, we found someone who's
excited and ready to answer all of your traffic related
questions.
Mike Knodler: My name is Mike Knodler, and I'm the director of
the Transportation Center at the University of Massachusetts, and
I'm a Professor of Civil and Environmental Engineering at
UMass.
Jane: Mike's job is all about helping people and things get
from one place to another safely and efficiently. When he was
little, Mike wanted to be a math teacher, but as he grew up, he
realized he wanted to focus more on applying mathematical
concepts to the real world to solve problems, and he still
teaches too.
Mike Knodler: So that was the switch to engineering, and then
within engineering, that's when I found transportation. I really
love it when we teach things in our classes and then see our
students go on and design or build that same thing, maybe in
other places, or if we're working on a design, and then
you see it get built. That's really, really rewarding. And if
it works as you intended, and you've potentially saved
someone's life, or you've made their life better because
they're able to get where they need to go. That's really,
really rewarding.
Jane: Of course, when we're talking about transportation,
it's way more than just cars on the road. We've made episodes
about trains and boats and bikes, and we'll link to all of
those in our show notes, but our episode today is going to be
about how we've developed the systems that help us know when
to go, when to stop, when to walk across a crosswalk, whether
you're a pedestrian or in a car, these things are really
important, and the systems are what help us be able to move
efficiently and safely. Now, speaking of moving, have you
ever been stuck in traffic in a car? I know lots of you have,
and maybe that's when you get your good But Why listening in
you've sent us a lot of questions about why we get stuck
in traffic.
Ben: My name is Ben. I'm five years old. I live in Rockville
Center, New York. Why is there traffic?
Lainey: Hi. My name is Lainey, and I'm six years old. I live in
Nashville, traffic?
Wallace: My name is Wallace. I live in Montreal. I'm seven
years old. And my question is, how does congestion get made on
the roads?
Mike Knodler: Yeah, so traffic, in terms of, you know, the build
up of cars, let's say, or, you know, creating a bit of
congestion, is when there's a lot of people that want to use
the same space at the same time. That's really the basic sort of
underlying cause of traffic. You know, it gets it gets a little
bit more complicated when we start talking about people that
might be in a car, versus walking versus on a bike, and
now you've got what we call mode, so we've got all these
different modes trying to use the same space at the same time,
and that causes that disruption in that traffic.
Jane: I live in a town that doesn't have any traffic lights.
We don't have any stores. We are a very small town, but we still
have stop signs, and we have some intersections where the
roads cross or a driveway comes in, where you have to know the
rules, even without a sign. So even for people who live in
rural places, there is usually some sort of infrastructure that
helps us be safe, or know who's going to go when, and some sort
of rules or ideas around how we can move around on the roads in
a way that allows all of us to go as efficiently as possible,
right? When did that kind of system start to develop?
Mike Knodler: Yeah, no, that's been that's been in existence
since people started navigating, a lot of even predates, you
know, cars in many, in many ways. And so it's all the signs,
the traffic signals, all the pavement markings that you see.
All of those are intended to help keep drivers and other
users of the system informed as to what they're supposed to do.
But more importantly, we're really talking about trying to
keep it orderly. And by keeping it orderly, we hopefully keep it
safe and then also keep it efficient.
Jane: What did those systems look like before we had cars?
Mike Knodler: Some of it goes back to horse and buggy days,
right? So when we used to have people navigating, and so some
of the early signage was referring to where you could and
couldn't ride, and what you couldn't couldn't do. And then,
obviously, with the introduction of the cars, we started to add
in things. But we had speed limits before we had cars as an
example, so people were limited in terms of how fast they were
allowed to go. And then as we've added more and more technology,
we've added more and more of the rules and the markings and the
devices that are intended to help keep the system orderly.
Jane: So were the speed limits for things like trains, or were
they even for how fast you could go on your horse?
Mike Knodler: Yeah, so I think you had some horse related ones.
And then obviously the early days of automobiles had speed
limits as well, and so there was definitely trying to keep
speeds, particularly in areas where same things we see now,
but in areas where you're likely to see somebody walking a
pedestrian, interact with somebody that might have been on
a horse or in a vehicle, you know, we know that that
difference in speed causes a safety concern. So how do we
control the speeds to make everybody safer in that
situation.
Jane: And eventually we got to traffic lights, and a lot of
kids have questions about traffic lights.
Ishan: Hi, my name is Ishan. I live in San Jose, California. I
am five years old. How do traffic lights work?
Evie: Hi, my name is Evie. I'm seven years old, and I live in
Rockville Center, New York. And my question is, why do we have
traffic lights?
Isadore: I'm Isadore. How do traffic lights work?
Alice: I am Alice. I am seven years old. I live in Salt Lake
City, Utah. How do traffic lights work?
Jackson: Hi. My name is Jackson. I live in Orlando, Florida. I'm
seven years old. How does a traffic light work?
Emily: Hello. My name is Emily. I'm six years old. I come from
London, UK. How the traffic lights work?
Sarah: Hi. My name is Sarah, and I'm from St Paul, Minnesota, and
I'm six years old. And my question is, how are traffic
lights made?
Mike Knodler: So the traffic lights are actually more than
100 years old now. So the patent goes back to the early 1900s,
1920 right around there. And again, they were all created
with the idea of keeping orderly flow. And so primarily the idea
of stopping one stream of traffic so that another stream
of traffic going in an opposite direction would be able to go.
And so some of the early traffic signals, if you look at them,
they're actually kind of unique. They were arms, and the arm
would go up and say, go, and then another arm would come up
and say, stop. And that was sort of the way that they work.
Jane: Not like a train arm, but smaller.
Mike Knodler: Yeah, no. So it was on a mast arm, so it would
be up on a regular pole, and then at the top of the pole
would be an arm that would raise up and say, stop, or an arm that
would raise up and say, go.
Jane: So that was before we had electricity, yeah, that we could
have on poles.
Mike Knodler: Yeah. And then now, now we have a lot more
technology and a lot more capability. And so we switched
to lights being sort of the primary measure by which we do
that. And then now we have a lot more complexity as well in terms
of what we've designed at intersections and some of the
different we call it the signal phasing. So what are some of the
different phasing things we can do where we maybe tell this
group of vehicles they can go, and hold another group back, or
maybe we tell the pedestrians they can go and stop all the
other traffic. And so there's a lot that goes into what we can
actually do to make them operate again with the idea of trying to
keep everybody safe.
Layelle: Hello. My name is Layelle. I'm five years old. I'm
from Phoenix, Arizona. Why does traffic lights always works by
themselves.
Alex: Hi, I'm Alex, and I'm seven years old, and I live in
Iowa. Why do traffic lights know when to go and to stop?
Elliot: Hi, my name is Elliot. I'm 11 years old. I live in
Great Falls, Virginia, and I would like to know how big is a
traffic light. How does it know when to go from red to yellow to
green and keep in sequence with all intersecting roads?
Isla: Hi, my name is Isla, and I'm four years old, and I live
in Vermont. My question is, how do stoplights know when to turn
green or red?
Max: My name is Max, and I'm five, and I live in Michigan and
and I want to know, why are traffic lights smart?
Jane: How do traffic lights know when to turn from green to
yellow to red and back to green by themselves, and how do the
traffic light patterns change depending on the amount of
traffic on the road or the time of day.
Mike Knodler: Yeah, yeah. No, that's so true. So on some
level, we actually can just make them what we call pre timed,
where the timing is just fixed, and no matter what, it's always
30 seconds of green for this street followed by 30 seconds of
green in the opposite direction. Perhaps that's, that's, that's
pretty basic. You know, there are some where we don't have the
technology in place to sense the traffic that's there, and they
might operate on that, that pre timed schedule. So that's that's
sort of basic, that might be in smaller locations where you
don't worry about sort of traffic flows building up, but,
but what's more likely now, a lot of the intersections that
you come up to have sensors. The easiest way to think about this
is that each of the legs of the intersection typically has some
relationship to the different sensing technology that's there.
And so if we, for example, for using an overhead camera, we
might be able to look and say, Hey, there's a car over here. As
soon as you get a chance, we need to bring the green back
over here, because there's a car waiting to go. That's that's
sort of the basic of how it works. But some of the sensing
technologies in the ground, sometimes we put it on some of
the legs of the intersection. Sometimes we put it on all the
legs. It's really a function of how much data we really need to
be able to make the best decisions for that, that traffic
signal, and how to make it work, and then not to add too, too
much, but now we actually go even further than that. We
actually can operate multiple traffic signals all together.
And so the traffic signals are talking to each other and saying
things like, Hey, I'm going to release a group of vehicles on
green, and they're coming your way. So you probably want to be
ready to turn on a green as soon as they get there in, you know,
and then we calculate out what the time is so, so the traffic
signals can coordinate in that way to be able to, again, try to
optimize it.
Jane: Now, when you describe it in my head, it makes me think
that there's like some person in either a building who can see
the cameras, or, you know, it sounds like there's some little
person in the traffic signal itself, saying, okay, now is the
time I'm going to release all those cars. But this is it's
not, there's not a person doing this.
Mike Knodler: No, not in real time. So in fact, you probably
drive by them hundreds of times and maybe never notice it, but
most of these signalized intersections that you would
drive by, if you look to one of the corners, there's probably a
cabinet, a metal box, on the side of the road, and in that
metal box, easiest way to think about it is there's a mini
computer, and that mini computer is really the brain of the
traffic signal. We call it a controller, and that's the
that's what's taking in all the input from the detectors and
anything else that might be operating at that intersection.
And then that's what makes the decisions that that the traffic
engineers would have programmed into the logic, saying, like,
Okay, here's here's what you can and can't do. Here's how you
should be thinking about it. And then that controller actually
implements it and runs it.
Jane: So in some ways, it's, you can think of it like it's all
kind of computer programming, and the computer programming
might have in its code something that says, If this happens, then
you do this. If this other thing happens, then you do this. So
it's, it's an automated system, but it is all coded for
different, what we would call variables, different things that
could happen in an intersection.
Mike Knodler: Yep, yeah, not all intersections have that, but,
but by and large, I'd say most of the intersections do indeed
have that. Where it'll it'll be able to go through, for example,
we're not going to put on a pedestrian phase at some
intersections if there's never a pedestrian that's there. But
then as soon as a pedestrian walks up and hits the pedestrian
push button, we'll turn on that pedestrian interval to give the
pedestrian some time to cross the street. So yeah, so the
traffic engineers are the ones that have a lot of that control
to be able to sort of program in the rules, and then the
controller actually makes it happen.
Jane: And you mentioned that one of the most important things is
to think about the different types of transportation, or
modes of transportation that might be using the same road or
the same intersection. And so when we think about that, there
are cars, there are trucks, sometimes there are trains that
cross roads. Lots of times there are people walking. We call them
pedestrians. There are bikes that use the same lanes as
traffic, but go at different speeds. Where I live, there are
sometimes horses that are using the roads, or people who are
using vehicles like tractors that are also allowed to use the
roads, but go at very different speeds. And so part of the job
of somebody who is a traffic engineer is to think about all
of the different types of vehicles and people on the
roads, and how to allow them all to use that road safely. That
must be something that you have to think really hard about.
Mike Knodler: Yeah, no, that's probably one of the more
challenging things, because, as you were hinting at, they all
have very different characteristics, you know. So,
for example, people walking, you know, might walk at one speed,
and that's much, much slower than somebody has the ability to
drive in a car. And a bike is probably somewhere in between
those two, obviously, in terms of the spin. So, so we're trying
to manage, you know, the amount of space they take up, coupled
with the speeds that they travel looking, coupled with where
they're looking to go at the same time and and managing what
we call those those conflicts is indeed one of the more
challenging things to think about from a transportation big
picture system perspective.
Jane: Transportation professionals like Mike think a
lot about human behavior when they design systems to keep us
safe, because whether we're talking about pedestrians,
people on bikes or drivers, it's the humans who are making
decisions and interacting with these traffic systems and
driving these big vehicles, and we humans sometimes get confused
or fail to follow directions or drive over the speed limit. So
it's Mike's job to take all of those possibilities into
consideration when designing a system to keep people safe.
After the break, we ask Mike, why does green mean go and red
mean stop, and why do we drive on the right side of the road,
at least in the United States? Stay with us.
This is But Why: a Podcast for Curious Kids. I'm Jane Lindholm.
Today we're learning about transportation systems with Mike
Knoedler, director of the Transportation Center at the
University of Massachusetts. Let's jump right back in with
your questions.
Josephine: My name is Josephine. I am seven years old, and I live
in New York. Why does green mean go and red mean stop.
Alonzo: My name is Alonzo. I'm four year old. I am from
Richardson, Texas. Why does green mean go?
Colette: Hi. My name is Colette. I am seven years old. I am from
Maryland. Why are traffic lights green, red and yellow? Why do
they choose those colors?
Mike Knodler: Yeah, so there's a lot that actually goes into the
actual design of traffic signals and the colors, and it's very
precise, in fact, but one of the reasons that red is associated
with stop is really two reasons. One, we tend to think of red
just being that, that damage, that danger, sort of, you know,
if somebody was bleeding, they're concerned, right? So, so
it has that, that already alarming message, which is, you
know, potentially good when it comes to thinking about traffic
signals. But the other, and the more important reason, is it's
more visible from further away. And so given how important red
is in a traffic signal, we want that to be the most visible. And
so as a result of that, that's one of the reasons that we ended
up with red. Now the other colors that ended up on there. A
lot of what we're actually thinking about is, how are
colors going to appear to people that might have color
deficiencies? So people that might be color blind. And so if
we think about some of the more common color blindness patterns,
we're trying to make sure that we're we're using colors that
are going to show up differently to people that might have
different color deficiencies. And so that's one of the
reasons, as an example, that red is always on the top. So even if
somebody can't distinguish between red and green, they can
see that the top section of the traffic signal is illuminated.
So they know that that's red. Or if they see that the bottom
section of the traffic signal is illuminated, they're going to
know that that's, you know, sort of the green. And so that's
another one of those human factor, there's things that we
take into consideration in the design of traffic signal
displays.
Arlo: I'm Arlo, and I'm from Durham, North Carolina. Why is
stop signs red?
Jane: And stop signs are red, and you talked about that color,
but stop signs, at least in the United States, are also always
one specific shape.
Mike Knodler: Yeah, so that's a really, really awesome question.
So the red, the cautionary message and being visible from
greater distances. But one of the reasons so that we we make
stop signs octagons, is so that they're really recognizable to
people. They know, whether they're in Massachusetts or
Florida or California, when they see an octagon, they know that
it's going to be a stop sign. The other reason that we use
that particular shape is, let's say that I'm on a roadway and I
look to the side street next to me. I can tell from the I can
tell from the back of the sign, that that driver has a stop
sign. So because it's a very recognizable pattern, that
octagon, I can look, if I'm on the main street, I can look and
say, Oh, the driver on the side streets going to stop, because I
know they have a stop sign. And so that's another reason that we
we use. So we use combinations of the letters or the symbols on
the sign as well as the shape of the sign as well as the colors
that are on the sign to communicate messages to people.
And each of them has an intended purpose.
Jane: Okay, but then what about the color yellow or amber?
Sometimes it seems like the adults around us think that an
amber light at a traffic signal means speed up really fast so
you don't get caught at a red that's not what it's supposed to
mean.
Mike Knodler: Yeah, so by nature, the yellow is intended
to imply a cautionary message. So when you see it, for example,
on a sign, it's usually warning you about some, you know, a
curve coming up, or some hazard that might be there on the
roadway. In a traffic signal when we see yellow, it tells you
that whatever was previously on is coming to an end. That's the
other meaning of that. That steady yellow is to tell you
what's happening. And you're right. Some people do say, I
know this means it's ending. I better speed up and go. And
that's that's not the way that we're intending it. But we do
want people to be able to get safely through the intersection.
Jane: Right? So if you're already in the intersection, the
message is, keep going, hustle up. It's going to turn red soon.
You don't want to be caught in the middle of the intersection.
Mike Knodler: Exactly. Yeah. So when we time that yellow in
between, we're really timing it so that if somebody had just
entered, they have enough time to be able to make their way
out.
Jane: And of course, these signals aren't just for drivers
as pedestrians, people who are walking or rolling or strolling.
We need to pay attention to the walk signal that tells us when
it's safe to cross the road and when you need to wait. In the
United States, the walk sign is usually an outline of a person
brightly lit up in white. Once the walk sign turns to flashing,
that's usually saying, if you haven't started crossing, you
should wait for your next turn, because you don't have enough
time to get to the other side before the traffic can start
going again. Sometimes there's even a countdown of numbers,
which is helpful so you know exactly how many seconds you
have left across the road.
Marley: Hi. My name is Marley. I live in Pinole, California, and
I'm eight years old. And my question is, why can cars go
past the speed limit if it's not allowed?
Mike Knodler: Yeah, this, this comes up a lot. Should we be
putting technology on vehicles that limits their speed? Or
should the roadway be able to communicate to the car, take the
human out of it, and tell the car you can't go faster than
this speed on this roadway? One of the reasons that cars have
that ability, though, is because of when, so the probably the
easiest way to think about this is, if you're merging onto a
highway, your car has to be able to get up to speed, or
accelerate up to speed really quickly. Well, that same thing
that allows you to accelerate, you know, if you're coming onto
the highway, to accelerate up to speed, to be able to merge in
with the traffic, and the highway is the same thing that
gives your car the ability to travel faster. And so that that
capability, that horsepower, that acceleration capability,
gives that vehicle, ultimately, that that speed capability.
Nicole: Hi. My name is Nicole, and I'm a mom from Wakefield,
Massachusetts. Why do we drive on the right side of the road?
Jane: And of course, here in the US, that's the side we drive on.
Mike Knodler: Yeah. So, so this one, this is actually goes back
to what we were talking about a little bit ago. Bit ago. So this
actually goes back before cars, back to the horse and buggy
days, and so when somebody was operating a horse, so a group of
horses, they would typically sit on the back left horse, and they
would sit on the back left horse, because it made it easier
for them to be able to, believe it or not, it's going to sound
really, really funny, two things, it kept it easier for
them to be able to navigate and keep the horses on track. But it
also if, back in the olden days, if they had to defend
themselves. Was they would be able to use their right arm to
pull out their their weapon and defend themselves. And so that
capability existed. And so then when somebody was on that left
side, they just made it easier, if the vehicles or the horses
and buggies that were coming at them were on the same so the
drivers were side by side with each other, you know, so left,
you know, left to left. And so that just became what we knew,
and then, and then that became how we we drive, and just became
the rules of the road, and the norm.
Jane: That's the rules of the road in the United States. And
if you drive into Canada or from Canada into the United States,
it's the same. You're probably driving a car that has the
steering wheel on the left side and you're driving on the right.
But if you're driving in some other countries, that is not the
case, and your car might look quite different. You might have
a steering wheel on the opposite side.
Mike Knodler: Yeah, no. And it's really, really such a weird
feeling, and it's a lot of historical carry over at this
point. And so you know you, as you look at country by country
across the world, the majority now drive right side of the
road, similar to what we have, but there are still some that
certainly do and and I don't envision them ever changing, or
at least anytime soon.
Jane: Let's talk a little bit about roads themselves and how
they work. Saoirse lives in Fletcher and wonders:
Saoirse: Why are some roads bigger than others?
Mike Knodler: So it kind of depends, right? So the easiest
way to think about this is every road has a function, or every
road has a purpose. So what's the purpose of that roadway? And
so some roads are maybe they're a really important roadway
because they link a town with a city, but then there's roads in
that city that link that city to a bigger city. And so when we're
expecting that there's going to be a lot of cars wanting to use
that road, we'll design a bigger road to be able to accommodate
more traffic. And then there's some other reasons too. So for
example, you know, we want to make sure that there's access to
all the places that need access. And so sometimes we might design
even though it might be, like you mentioned that you live in a
smaller town, rural area, but we still want to make sure that
there's the ability to get where people need to go. And so we
might design a road that would be able to accommodate that. Now
roads might get bigger if we want to add bike lanes or if we
want to add sidewalks. So those are some of the decisions that
we make with saying, Okay, how much space do we actually have
available to us?
Hazel: My name is Hazel, and I'm six year old, and I come from
Canada, Ontario. Why are there so many cars on the highway?
Mike Knodler: Yeah, that's, I mean, that human decision making
is really at the heart of it all. So when we make it easier
for people to be able to travel in their car, then we, as a
result of that, end up with more cars on the roadway. And so
that's, that's really, so there's, there's obviously we,
as we make it easier for people to travel in their cars, you
know, we get more, but we still see people traveling in their
cars even when they know that they're going to be sitting in
traffic. And part of the reason for that might be that people
want to have their car with them because they maybe they need to
leave, you know, by a certain time it goes somewhere, or they
have to pick somebody else up, or, you know, they might have
some other thing that they have to do, but also, and this is
where, you know, we could debate, sometimes, when we build
up roadways to the extent that we do, we're not necessarily
thinking about, well, what other options that people have? And so
this becomes a really big push to say, well, let's design
better bike infrastructure, let's design better public
transportation if people want to take a bus or a train. If we
design those systems, will we end up with less cars? And
oftentimes the answer is yes. So we're trying to figure out what
the balance is in terms of where to invest the money that we have
building the infrastructure that people need or want to have
based on where they where they live and where they want to go.
Jane: Yeah, it's also interesting, because there are
so many interlocking pieces that need to be in place for people
to be able to live their lives in a way that allows them to do
everything they need to do. And cars, for many of us, are a big
piece of that. But for some of us, we don't have cars, or we
feel like we can't get a get around without a car, like when
I used to live in a big city and I didn't have a car, but the
nearest grocery store was five miles away, and I could only get
a few groceries if I was going to take the bus back home
afterwards. So thinking about how all of these pieces fit
together is a really important part of being an engineer of
certain kind of engineer, or a designer, or thinking about city
and town infrastructure, and if that interests kids, that might
be a great career to go in.
Mike Knodler: Yeah, and what's really and what's even more fun
now is we're starting to see a lot of different modes emerge.
So the example you just gave is you live in a city. And you want
to go to the grocery store, but you can't carry five bags of
groceries on the bus or the subway, for example. But now
there's companies that make electric cargo bikes, and so now
you can actually rent a cargo bike or own a cargo bike for the
day and take the cargo bike to the store and be able to fit
your five bags of groceries and then go home, but not take up
the same amount of space as a car, for example. And so one of
the things that excites me now, and some of the challenges that
the students today might encounter in the near future, is
thinking about what some of those technological innovations
are that solve some of these problems that we're talking
about.
Noah: My name's Noah, and I'm five years old, from Louisville,
Kentucky, and my question is, how do roads carry cars without
breaking.
Mike Knodler: Yeah, that's there's a whole science that
goes into this. You could actually make an entire career
studying roadways. And so, for example, think about airports.
It's kind of the same exact thing, but they're carrying much
heavier vehicles and expectations. So so the design
is really saying how much weight is that roadway going to carry,
and then based on that weight, we'll govern a couple of things.
So what types of materials we might use to build that roadway,
and then oftentimes, how thick it is. So when we put together
the types of materials with the thickness that gives us a
strength. And so we're able to say, based on this anticipated
load of weight, what what strength of roadway do we need?
And then we construct that roadway with that strength so
that we're able to make sure that the road doesn't break.
Jane: It's not something that you would probably look for
unless you're specifically keeping an eye out for it. But
kids, if you're riding in the car or on a bus, and you look at
the road sign, sometimes you will actually see a sign that
tells vehicles how much weight they're allowed to have to be on
that road. There is often a weight limit on a road, and it
will say, you can, you cannot bring your truck on this road if
it weighs more than, you know, 28,000 pounds, or whatever the
road limit is. And in, again, in my town, some of our roads are
dirt, and so at certain times of the year, heavy trucks aren't
allowed on the road, but they are allowed along on the road
when it's dry, or in the winter when it's frozen.
Mike Knodler: Yeah, no, though. So the so a lot of times we
think about bridges is a good example where obviously there's
a weight concern at bridges, roadways themselves, and then on
the highways. Sometimes, when you're driving on the highways,
you'll see weigh stations where the police or similar, will be
out there weighing trucks, because the single fastest way
to destroy a road is to have an overweight truck drive on that
road. It will, it will really break the material and break it
down so that it ruins the roadway. Because once the
roadway gets ruined, it's really, really hard to fix it.
Jane: Well, both Hannah and Evelyn have noticed that
sometimes roadways don't look as good or operate as well as they
should.
Hannah: My name is Hannah. I'm five years old, and I live in
Roswell, Georgia. How does the road get cracks in it?
Evelyn: My name is Evelyn. I live in Philadelphia, and I'm
five years old. And my question is, why are roads sometimes so
bumpy?
Mike Knodler: When lots of cars go over that roadway all the
time, and at the same time that pavement, or that roadway
section, is having to sort of handle the elements of the
weather. So sometimes it gets water on it, then the water goes
into the pavement and then freezes, so it starts to break
the pavement apart a little bit, and you put all these together
and then at the same time, and this is one that people don't
actually see. There's material underneath the ground. So the
when it freezes, it actually starts pushing up on the roadway
from the bottom. So we think about what the traffic is on the
top, but the roads are sort of fighting from the bottom as
well. Because, you know, as the temperature changes, the soil
does some really interesting things as well. So, so that's
what leads to cracks and potholes. And a lot of the
deformations that you see is just the amount of loading that
you'll, you'll, you'll regularly see as part of that. And then,
you know, we can go out and we can do some maintenance to help
sort of make roads last longer. But one of the things is it
costs money, and so, you know, we don't always have the money
available to go out and fix the roadways as soon as there's a
crack. So usually, when you see one crack, you know that there's
going to be another crack before long, and then there'll be
another crack, and then you hope you're able to make the repair
before you have to just fully redo the roadway. And so, so it
becomes a bit of a game, trying to figure out when to do what,
and then what to do specifically.
Jane: Transportation is something that affects every one
of us, and it's thanks to people like Mike that a lot of times we
don't even think about the systems, even though they're all
around us. Mike says one out of every ten jobs in the United
States is related to transportation, which just goes
to show how important these systems are in helping to make
sure people and things get where they need to go safely and as
speedily as is allowed. Thanks to Mike Knoedler for answering
all of our transportation questions. As always, if you
have a question about anything, have an adult record, you asking
it on a smartphone using an app like voice memos, then have them
email the file to questions@butwhykids.org. Uur
show is produced by Sarah Baik, Melody Bodette, and me, Jane
Lindholm at Vermont Public and distributed by PRX. Our video
producer is Joey Palumbo, and our theme music is by Luke
Reynolds. If you like our show, please have your adults help you
give us a thumbs up or a review on whatever podcast platform you
use, it really helps other kids and families find us. We'll be
back in two weeks with an all new episode. Until then, beep,
beep. Stay curious.