May 10, 2010 • 28 mins
We often take traffic lights for granted, but regulating the flow of traffic takes a lot of planning and technology. Jonathan and Chris detail the technology behind traffic lights in this episode.
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Speaker 1 (00:00):
Brought to you by the reinvented two thousand twelve camera.
It's ready. Are you get in touch with technology with
tech Stuff from how stuff works dot com. Hello again, everyone,
welcome to tech stuff. My name is Chris Poette and
(00:20):
I am an editor here at how stuff works dot com.
As usual, sitting across from me is the lovely smiling
face of senior writer Jonathan Strickland. Do go on now,
I think I should stop nice hammer time. All right?
This uh, this episode is brought to us courtesy of
a little listener mail. This listener mail comes from Nate.
(00:46):
He says, Hi, I'm a teenage listener from Colorado and
just received my learners permit. I'm often frustrated by stoplights
that are too long or short for the intersection. That
got me wondering about how these things actually work. So
I'm hope thing that you can do a podcast on
how stop lights work. Thanks from your best listener in Colorado, Nate. Alright, Nate,
(01:07):
we're gonna talk about some some traffic lights. Yes, and
uh do you like traffic lights? I like traffic lights
only when they're green. Apparently Nate does. Alright, so um, well,
let's you know we all know what traffic lights are.
I don't think we need to do the breakdown that
we usually do. Yes, Uh, It's it's funny because when
(01:31):
this email came in, I started thinking, Um, you know
how very simple this idea is. You know, you've got
a box and it's got some lights in it, and
they have very red light or yellow light and green
light at least here in America, and they switched from
one another. Well that's pretty simple. Then I thought, well,
you know, there really is a lot more to it
than that, because it's not just the lights, it's also
(01:52):
the controller in the whole system that goes behind it. Yeah,
especially when you look at it from a macro level
like a city, a city size level, it becomes unbelievably
complex because you're not just talking about one intersection. You're
talking about traffic patterns that go across an entire city. Well, yeah,
and you can use uh, if you've got the system
that can handle it, you can use uh, you know,
(02:14):
a whole computer network of traffic lights to uh to
arrange the way traffic would flow. That is, assuming everybody
is obeying the law right. Well, and and that's important
to remember because you know, in the old days, making
adjustments to traffic lights was pretty difficult, I mean, or
at least it was more involved than what it is today. Today.
(02:36):
You know, there are fully automated systems where you can
walk into a room and see the redoubts and kind
of get a real life, real time picture of what's
going on. And if traffic is really bad in one
part of town for one reason or another, you can
actually make adjustments on the fly in many systems and
and alleviate some of that traffic snarl. And and that's
(02:58):
and it's crazy the sort of things that cause traffic jams.
I've written about how traffic works for the site article.
It's and it's really things that you would never expect
to cause traffic jams can in fact cause them. And
sometimes it's just poorly timed intersections. You know, you could
have two intersections that are even a mile and a
(03:19):
half apart, but because of the way they're timed, traffic
starts to back up. So we're gonna talk a little
bit about what goes into making these lights work. I
wanted to to step back a little bit and talk
about the the older systems because some some towns in
in the United states still use these. Before the solid
state electronics controllers for traffic lights became really the thing,
(03:44):
we had mechanical controllers. Now, the lights themselves are electrical,
and they're also modular in most cases, so that you
can build a larger set of lights using the same
basic units, so that lets you do things like create
the you know, the turn signal lights versus the straight
up and down you know, red yellow green lights that
(04:06):
we we know and love. Um Now, the old lights
were halogen lamp lights, but usually between fifty watts and
a hundred and fifty wats, depending on the size of
the light. I would I would have thought that they
would be incandescent, did you I would have you would
have Apparently I would be wrong. Well, the current ones
are LEDs. Yes, they're much more efficient, and you can
(04:29):
tell those apart two because it looks like they're a
batch of little tiny lights in the circle where an
older one of the older lights would be with the
giant limbs. Right, So these older very cool that they're
doing that because there's so much more energy efficient. No, yes,
they're energy efficient, and you don't have to replace them
nearly as often the old ones. You would actually have
(04:50):
to replace almost on a monthly basis, which of course
could cause even more problems with traffic because it means
that someone has to guts to go out there. And yeah,
so these older MCCA Nicole controllers, they actually if you
were to open up one of these boxes, here's where
we have our standard, do not open a traffic control box.
It's a bad idea, but probably against the law if
(05:13):
you're not exactly Oh well, if you're authorized to do it,
then yes, by all these please yes. But inside these
mechanical controllers, you would find a series of switches, uh.
And at the base of each switch would be a
little wheel. Now the wheel would have uh, twelve sections.
Think of it like pi. So it's got essentially a
(05:35):
twelve twelve areas sliced and one slice has been removed.
When that slice comes round towards the switch, the switch
is actually able to move out and the the switch
uh completes a circuit. All right, So there's a circuit
for every single light at the intersection, for the red light,
for the yellow light, green light, for each of the
(05:56):
directions that are involved. Okay, this is a four wast yes,
so four away stop. You know you've gotta you've gotta
switch for every single light. Uh So these these the
series of wheels are on a rod and they turn
um in time with a solenoid. The solenoid activates, it
(06:17):
turns the wheels and then that's what actually completes the
circuits and make the different lights switch from red to
green to yellow. Makes sense. Um, these solenoids on a ratchet,
so it can move down, but it can't move back
up right, So it's not it doesn't justn't go from say,
(06:38):
yellow to green. It has to go from green to
yellow exactly. And you also don't have to worry about
it switching from green to red and then back to
green immediately, because that would happen if if if it
didn't have the ratchet, if it didn't have that breake
stop there. Um, a light could change and then change
right back, and then you've got traffic accidents all over
the place. Uh So we got enough of those with
(06:59):
it work properly. Right. So, the solenoid is connected to
a motorized timer, and the timer is this little round drum.
It's got a hundred grooves carved into the side of
this drum. Right within those grooves, you can place these
little metal tabs, and the metal tabs also hit a
little switch. When the tabs hit the switch, that's what
(07:21):
activates the solenoid. Okay, so the drum is attached to
a gear. The gear turns at a certain frequency, certain
number of revolutions per minted. That's what dictates how fast
the drum turns. That's what dictates how how often the
solenoid is activated, which in turn dictates how the little
wheels connected to the circuits turn. That is the timing
(07:43):
mechanism on the old UH traffic lights. And if you
were actually standing next to a controller box and you
were listening, you could probably hear the clicks as those
wheels turned into place. Um and UH. You could even
install multiple drms within a single control box, so you
could have it switch at different times of the day.
(08:04):
So let's say during rush hour traffic you need one
section of the road to be green more often than not.
But then in the middle of the day the traffic
patterns change, so you would want the light behavior to
change as well, and then maybe overnight it changes again. Um.
You could actually do that by having multiple gears in
there and have it switch automatically from one to the
(08:24):
other based upon the time of day. Today, all of
that is kind of it's it's antiquated. I mean, you
don't find that in most systems today because now we
have solid state electronics. Everything's on circuit boards. We don't
have to worry about all those uh those actual mechanical
switches right right, But some of them are still on timers. Yeah,
(08:44):
that's true. That's true. You know when you describe things
that run on gears like that, I'm trying to picture
exactly how this hardware goes together. I can't help singing
Powerhouse in my head when I imagine the gears turning right. Uh.
That okay, so and and Marshall actually wrote a blog
(09:04):
post about this where he links to a video where
you can see. If you want to go to the
to the blogs how Stuff Works and search marshall brains
blog posts, you can find a post that links back
to a video that shows these elements, these mechanical elements. Yep, yep,
I remember that one. Actually I saw that as I
was doing some some research. Um. Now, of course, uh,
(09:27):
you know there are timers, and there are the uh,
the lights that work on a sensor system as well.
Um and the timers seem like they're fairly self explanatory. Yeah,
it's it's a state timer instead of mechanical same same
philosophy as the mechanical ones. But yeah, different different methodology,
but same effect. And that, Um, what happens. You've got
(09:48):
some civil engineers who who observed the traffic patterns, who
come up with the the pattern that should be used
for any particular intersection, the amount of time that each
lane of traffic should have to be able to pass
through that intersection. And um, you know, normally they will
visit an intersection multiple times throughout different days to really
(10:10):
get a good idea of what the traffic patterns are, because,
like I said, they changed throughout the day, right, So
in the evening it may be that, you know, one
particular road is hardly a used all while another one
is is really heavily used. You would want, of course,
the traffic light to favor the heavy use one. Um.
And again this is it sounds kind of simple, except
(10:31):
that when you take into account that you need to
also look at the intersections that are essentially directly adjacent
to that first intersection, like go in in every direction
of that intersection to the next light and see what
that timing is, because that's gonna affect the traffic as well. Well.
Then you have to go one further out from those,
(10:52):
and before long you're looking at a huge net that
incorporates the entire area, which is why it gets so complicated. Um,
but not all of them are timers. Some of them
use sensors, and these are the ones that I find fascinating.
You can you can tell whether or not they have
a sensor generally by looking at the uh not up
(11:13):
where the traffic lights are, but down on the road. Yeah. Um,
there are different kinds of sensors. There are some intersections
they'll use light based sensors like lasers or well, but
but most, in fact, I would I would go so
far as to say the majority of all sensor sensors
used in traffic lights are inductive loop sensors. Yes, that's
(11:34):
the ones that you see, uh, the little grooves in
the pavement directly underneath, like the white stripe where you're
supposed to stop your car generally or or immediately before
in some cases immediately after, which I think is kind
of dangerous if that's the sensor that you're supposed to
be on to trigger the light. But that has to
do with the civil engineers, or perhaps they were painted
(11:54):
by uncivil engineers. Could be UM, but we wonder why
is the Civil War even called that because they were
not UM. So the sensors that are implanted underneath the
roadway act very much like an electromagnet. Yeah, that's essentially
(12:15):
what they are. They You've got a coil of wire
that is underneath the pavement and m and what it's
it's generating a magnetic field and when something really large
and metal passes over it, it acts as an inductor.
And when the system uh can detect that that increase
(12:37):
in the magnetic field. Because once you have the inductor there,
that really boosts the magnetic field. Wants the system detects that,
it's the indicator to say, hey, there's a car waiting
at this intersection, so at the earliest opportunity we should
look at switching the light so that the car can move. Um.
There's some problems with this system though, Yes. The big
(13:00):
this problem being that if you are not in a
fairly you know, like a medium to too larger sized vehicle,
you may not have enough of metal in the mass
of whatever vehicle you're in to to activate the inductor loop.
So what you're saying is, if you were in our writing,
say a motor scooter, motor scooter, bicycle, motorcycle, even even
(13:24):
a small car like a smart car. Smart cars are
tiny and may not even be enough of a mass
in order to get the inductor loop to activate. It
may not generate enough of a magnetic field for the
sensor to be tripped, which means you're sitting at a
traffic light forever waiting for that thing to change, and
it may take until another car or other vehicle pulls
(13:47):
up behind you and perhaps if they're close enough, complete
that that inductor loop so that you can actually trigger
that light. UM and another or of Marshall's brains posts
that that I saw when I was looking at UM
looking at some information for this podcast. UM. Some cities
(14:09):
do have special infrared controllers too for emergency vehicles like
fire engines and police cars, UM, that will allow them
to trip the signals before they get there. It's it's
essentially a remote control of sorts that allow them to
UH to affect the signals and that that keeps them
from having to of course, they're going to go to
(14:30):
the light anyway if they feel like it's safe. But
if they can go ahead and change the traffic lights
rather than having to go through the intersection without affecting
those at all, that that helps them control the flow
of traffic too to some extent. I have a hint
for people who do drive motorcycle, scooters, bicycles, that kind
of thing, if they want to activate those loops. Uh.
(14:52):
This is not the same thing that Chris was just
talking about. Chris was talking about actually changing the light
signals in an official way. Just activating yeah, to let
to let essentially to let the system know, Hey, I'm
here and I would very much like it if I
could get across the street please. Um. What you can
do is you can install a couple of magnets on
(15:12):
the bottom of your vehicle. Uh. And by installed it
just means stick because that's the one thing about magnets.
They stick to metal. Uh some metal, so, yes, well
the metal that you typically find in vehicles. Yes. Uh.
So you get a couple of powerful magnets and you
attach them to the base of the vehicle, and then
when you when you drive over the loop, the magnets
(15:35):
in there, they usually generate a strong enough magnetic field
that that will be enough to trip the sensor and
let it know, hey, there's a vehicle here. So even
if you're just writing in a little scooter that normally
wouldn't activate it, you'll get a signal. Now, these systems
are connected, as we said earlier, to a master control system,
(15:56):
and the master control system's job is to maintain an
on everything that's going on across the the whole uh well,
whatever the area is that it that they oversee, whether
it's a local like thing or a citywide thing, um,
but it usually it monitors traffic twenty four hours a day.
Often these systems can be manipulated remotely so that, let's
(16:19):
say that that the the operator knows there's a fire
uh a fire alarm that's gone off in a building downtown,
and they know where the the fire engine is going
to come from. They can actually proactively uh uh set
up the system so that it stops traffic so that
the fire engine can get through without any dangers of
(16:40):
or reducing danger of collision. I can't ever say without
any because there's always gonna be some something that falls
outside the extremes, right um. And they can also just
keep an eye on how signals are behaving and if
they if there's a signal oiled edge or anything like that,
they can arrange for an electrician in or or you know,
(17:01):
repair unit to go out there and take a look
at it. Um. And they have to consider a lot
of things when they're putting light. As we said, when
they're putting these traffic lights in, it's everything from the
spacing between the traffic signals along the street. Um. They
have to look at the different timing aspects of each
of those. They have to look at just the traffic volume.
(17:21):
How many lanes of traffic are there. Is it going
to to handle the traffic volume well enough so that
you don't have to worry about fiddling with the timer
so much? Um, even the driver behavior on that street.
Because of course, Chris and I know from living in Atlanta,
there are different parts of Atlanta where people drive in
(17:42):
incredibly different ways. Let's say, like to eight five. If
you're not going to eighty miles per hour, you've just
been run over. Now, granted to also does not have
any traffic lights on it, but um, yeah, there's surface streets,
Like there's certain areas of Atlanta where you know, people
drive nice and leisurely and and everyone's kind of you know,
laid back and relax in other parts of Atlanta where
(18:04):
you feel that, you know, you've just entered the road
warrior and two men will enter and one man will leave,
and you know, Mel Gibson's right behind you and burying
it down. And Okay, I've had some really really weird
dreams lately. As all I'm trying to say, I understand
which so yeah, the driver behavior actually does play a
part in how traffic managers look at at setting out
(18:25):
traffic lights and timing them out properly. Um. And it
seems to me that that, um, if you've got lasers
or inductive loops or uh you know, even those rubber
air filled rubbered hoses I guess they're pneumatic hoses of
some kind that uh tell the box that their cars waiting,
it seems like including those would sort of wreck the
(18:46):
plan of trying to manage traffic I mean other than
I mean and by by a master control program. M.
Wait a minute, I'm beginning to understand everything and of line. Um,
but no, yeah, having a master computerized program, uh, it
seems like it wouldn't work. It wouldn't be compatible with
(19:08):
having sensors at individual intersections that allowed cars to trip
the lights as soon as they arrived and we're sitting
there at the stoplight. It seems like it would be
more it's more sort of a if you will, lazy
fair version of traffic. I think they'll make the lights work.
I think part of it. I think part of this
that when that detects that there's a car there, um,
(19:28):
it doesn't necessarily say okay, well we need to change
the lights now. It's it's saying, okay, we need to
change the lights at some point when it's safe to
do so. Keep in mind that if they're steady traffic
going over an intersection, that and that inductor loop, actually
it's picking it up because of course you're still having
cars going through. So these systems are are fairly intelligence
(19:49):
probably the wrong word to use, but they're they're able
to detect traffic at uh if it's if everything's working properly,
they're able to detect traffic and a fairly rely I
will rate. So it's still it's not as planned out
as maybe the timed ones are in the sense of
it doesn't take as much human intervention. But there's still
(20:11):
you know, it's kind of it is kind of adjusting
traffic on the fly. But as I should point out that,
I realized that as soon as you pull up, it
wouldn't necessarily trigger the sensor and automatically turn the light,
because if the box can tell that there are there's
a steady flow of traffic going over the inductors in
the other lanes perpendicular to the ones that you're in, um,
(20:34):
obviously it's not gonna go, oh, well, hey, you know,
I'm just gonna go ahead and stop them. This one
guy really needs to go, so we're gonna stop everybody else.
I sort of always figured that it was a situation
where they go, okay, well it's been ten seconds since
the last car, it's been fifteen seconds since last car.
Traffic is slowing down, there's less of it there. It's
safe to go ahead and give them a yellow light
(20:54):
to prepare them for a red light. And some of
them work on a on a combination of the timer
and the sensor, so some of them have like even
in some cases you'll you'll come up to traffic lights
that you know have the sensors in them, and yet
the traffic lights occasionally change on their own because that
they do ultimately rely on a timer system. Um. And
the anat thing about those timer systems you can actually
(21:16):
program them so that they behave differently on different days
of the year. So if you know, for example, that
say on fourth of July, that a particular stretch of
road is going to be really heavily used, you can
program the system ahead of time to compensate for that
before you know, like you know, back in June you
could you could program it in and then fourth of
(21:37):
July comes around and the system behaves just as you
told it to, so that everything's working properly. Um. Cool, Well,
I'm trafficked out. Well, I think it's a it's one
of those things that we sort of take take for granted.
But the the systems that they've put in to make
this work, um, and try to be sort of intell
(22:00):
gin about the way you manage traffic flow. I mean,
it's obvious anytime there's been a bad storm and the
and the lights are out, how much work actually goes
into planning out the traffic patterns of a city. And uh,
the effect that having those sensors tripping the lights and
and letting the boxes, the controller boxes know what's going
on in an intersection. It's it's obvious how much difference
(22:21):
that makes having that technology available to us, particularly in Atlanta,
where people seem to forget that if the traffic light
is out, you treat it as a four way stop. Yeah, so,
Or when they're flashing yellow on one side and you're
supposed to proceed with caution versus flashing red, which means
you're supposed to come to a complete stop, right and
everybody stops regardless, or if it's flashing yellow, people don't
(22:41):
slow down at all. They're just like that means go,
that means actually go really fast. Yeah, if you're if
you're a starman. Yeah, okay, I've got nothing for that.
If you got that reference right in at tech stuff
at how stuff works dot com, or if you have
any other questions for that matter. But speaking of other questions,
I actually have another listener mail. This listener mail comes
(23:09):
from Trevor, and Trevor says, Hey, Chris and Jonathan, I
just finished listening to your podcast about cyborgs and cybernetics,
and it made me think about a recent book i've read,
Revelation Space by Alistair Reynolds is an excellent example of
advanced cybernetics. UH, pertinent throughout the book. I just thought
I would write and give you that book. Keep up
the good work, Trevor. PS. I know you constantly talk
(23:31):
about virtual environments, but how come I've never heard anything
from you about Second Life. I'm an avid member and
I'm curious why you avoid it. Well, Trevor, it's not
that we're actively avoiding Second Life, at least not more
than anyone else's. UM. Second Life is a virtual environment.
It's kind of think of it like a massively multiplayer
online role playing game without the game. Yes, I mean
(23:53):
you can create games within Second Life, but there's no
game element directly involved. There's no object of winning, there's
nothing like that. It's not you know, but you do
create an avatar and you can wander around a virtual
world and own virtual property and interact with other people
who are also in this world. UM. When it first premiered,
(24:13):
it actually made a big splash. You remember that, like
all the companies that were getting into it. Yes, there
were a lot of companies getting into it. There were
a lot of other organizations trying to uh, trying to
find ways that they could offer their services in the space. Uh.
You know, and I know for a fact that some
libraries were opening virtual reference desks in second life so
that they could, you know, have people come in and
(24:34):
ask them questions. There were bands that would have virtual
concerts and second life. Um. Yeah, you would find things
like I think a lot of news agencies built like
news desks in second life where you could you could
wander into this virtual environment and kind of see what
was going on in the real world. Uh. It was
an idea of like places where people could have virtual meetings,
(24:55):
where you could have maybe a conference online and have
people show up in second life to attend the conference,
and you wouldn't have to leave your home, right. A
lot of interesting ideas. It just never really took off
to the It never lived up to the potential it had. Um,
people still use it, but it's lots and lots and
lots of people still use right, but nowhere near the
(25:17):
number of people that everyone thought was going to use it.
Like a lot of the companies that went in and
spent money developing this stuff have since long since abandoned
those those stations within second life, just because they weren't
you know, it didn't make sense to keep supporting something
that was getting so little traffic. So that's really the
(25:37):
reason why we don't talk about Second Life. It's not
that we have anything personally against it. In fact, I've
written an article about how Second Life works, but it's
just that it really didn't. It doesn't have the impact
that uh, that it potentially could have, and so it
just we just don't end up talking about it. But
(25:57):
if you have any other questions, like I said, tech
Stuff at how stuff rex dot com. And remember we
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(26:17):
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and things, you can give us some feedback there as well, right, yeah,
and we really do like the audience interaction. It's it's
(26:39):
becoming increasingly more important to us. So please if you
have different ideas, you want to suggest something for the podcast.
Uh you think that maybe, for example, we're talking about
the possibility now, this is a possibility of looking at
h at some point interviewing other people on the podcast
every now and then. If you have ideas of who
(27:01):
we should talk to, give us a shout. Let us know.
Remember we're pretty low on the grand scheme of things.
So if you're saying Steve Jobs, keep dreaming, I want
to interview Benjamin Franklin. Yeah, I had a lot to
do with tech. I'm sending Adele Lovelace. Oh, should be
another good person interview. Yeah, all right, Well that wraps
(27:25):
this discussion up. I hope you enjoyed it, and Chris
and I will talk to you again really soon. If
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(27:46):
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Brought to you by the reinvented two thousand twelve camera.
It's ready. Are you get in touch with technology with
tech Stuff from how stuff works dot com. Hello again, everyone,
welcome to tech stuff. My name is Chris Poette and
(00:20):
I am an editor here at how stuff works dot com.
As usual, sitting across from me is the lovely smiling
face of senior writer Jonathan Strickland. Do go on now,
I think I should stop nice hammer time. All right?
This uh, this episode is brought to us courtesy of
a little listener mail. This listener mail comes from Nate.
(00:46):
He says, Hi, I'm a teenage listener from Colorado and
just received my learners permit. I'm often frustrated by stoplights
that are too long or short for the intersection. That
got me wondering about how these things actually work. So
I'm hope thing that you can do a podcast on
how stop lights work. Thanks from your best listener in Colorado, Nate. Alright, Nate,
(01:07):
we're gonna talk about some some traffic lights. Yes, and
uh do you like traffic lights? I like traffic lights
only when they're green. Apparently Nate does. Alright, so um, well,
let's you know we all know what traffic lights are.
I don't think we need to do the breakdown that
we usually do. Yes, Uh, It's it's funny because when
(01:31):
this email came in, I started thinking, Um, you know
how very simple this idea is. You know, you've got
a box and it's got some lights in it, and
they have very red light or yellow light and green
light at least here in America, and they switched from
one another. Well that's pretty simple. Then I thought, well,
you know, there really is a lot more to it
than that, because it's not just the lights, it's also
(01:52):
the controller in the whole system that goes behind it. Yeah,
especially when you look at it from a macro level
like a city, a city size level, it becomes unbelievably
complex because you're not just talking about one intersection. You're
talking about traffic patterns that go across an entire city. Well, yeah,
and you can use uh, if you've got the system
that can handle it, you can use uh, you know,
(02:14):
a whole computer network of traffic lights to uh to
arrange the way traffic would flow. That is, assuming everybody
is obeying the law right. Well, and and that's important
to remember because you know, in the old days, making
adjustments to traffic lights was pretty difficult, I mean, or
at least it was more involved than what it is today. Today.
(02:36):
You know, there are fully automated systems where you can
walk into a room and see the redoubts and kind
of get a real life, real time picture of what's
going on. And if traffic is really bad in one
part of town for one reason or another, you can
actually make adjustments on the fly in many systems and
and alleviate some of that traffic snarl. And and that's
(02:58):
and it's crazy the sort of things that cause traffic jams.
I've written about how traffic works for the site article.
It's and it's really things that you would never expect
to cause traffic jams can in fact cause them. And
sometimes it's just poorly timed intersections. You know, you could
have two intersections that are even a mile and a
(03:19):
half apart, but because of the way they're timed, traffic
starts to back up. So we're gonna talk a little
bit about what goes into making these lights work. I
wanted to to step back a little bit and talk
about the the older systems because some some towns in
in the United states still use these. Before the solid
state electronics controllers for traffic lights became really the thing,
(03:44):
we had mechanical controllers. Now, the lights themselves are electrical,
and they're also modular in most cases, so that you
can build a larger set of lights using the same
basic units, so that lets you do things like create
the you know, the turn signal lights versus the straight
up and down you know, red yellow green lights that
(04:06):
we we know and love. Um Now, the old lights
were halogen lamp lights, but usually between fifty watts and
a hundred and fifty wats, depending on the size of
the light. I would I would have thought that they
would be incandescent, did you I would have you would
have Apparently I would be wrong. Well, the current ones
are LEDs. Yes, they're much more efficient, and you can
(04:29):
tell those apart two because it looks like they're a
batch of little tiny lights in the circle where an
older one of the older lights would be with the
giant limbs. Right, So these older very cool that they're
doing that because there's so much more energy efficient. No, yes,
they're energy efficient, and you don't have to replace them
nearly as often the old ones. You would actually have
(04:50):
to replace almost on a monthly basis, which of course
could cause even more problems with traffic because it means
that someone has to guts to go out there. And yeah,
so these older MCCA Nicole controllers, they actually if you
were to open up one of these boxes, here's where
we have our standard, do not open a traffic control box.
It's a bad idea, but probably against the law if
(05:13):
you're not exactly Oh well, if you're authorized to do it,
then yes, by all these please yes. But inside these
mechanical controllers, you would find a series of switches, uh.
And at the base of each switch would be a
little wheel. Now the wheel would have uh, twelve sections.
Think of it like pi. So it's got essentially a
(05:35):
twelve twelve areas sliced and one slice has been removed.
When that slice comes round towards the switch, the switch
is actually able to move out and the the switch
uh completes a circuit. All right, So there's a circuit
for every single light at the intersection, for the red light,
for the yellow light, green light, for each of the
(05:56):
directions that are involved. Okay, this is a four wast yes,
so four away stop. You know you've gotta you've gotta
switch for every single light. Uh So these these the
series of wheels are on a rod and they turn
um in time with a solenoid. The solenoid activates, it
(06:17):
turns the wheels and then that's what actually completes the
circuits and make the different lights switch from red to
green to yellow. Makes sense. Um, these solenoids on a ratchet,
so it can move down, but it can't move back
up right, So it's not it doesn't justn't go from say,
(06:38):
yellow to green. It has to go from green to
yellow exactly. And you also don't have to worry about
it switching from green to red and then back to
green immediately, because that would happen if if if it
didn't have the ratchet, if it didn't have that breake
stop there. Um, a light could change and then change
right back, and then you've got traffic accidents all over
the place. Uh So we got enough of those with
(06:59):
it work properly. Right. So, the solenoid is connected to
a motorized timer, and the timer is this little round drum.
It's got a hundred grooves carved into the side of
this drum. Right within those grooves, you can place these
little metal tabs, and the metal tabs also hit a
little switch. When the tabs hit the switch, that's what
(07:21):
activates the solenoid. Okay, so the drum is attached to
a gear. The gear turns at a certain frequency, certain
number of revolutions per minted. That's what dictates how fast
the drum turns. That's what dictates how how often the
solenoid is activated, which in turn dictates how the little
wheels connected to the circuits turn. That is the timing
(07:43):
mechanism on the old UH traffic lights. And if you
were actually standing next to a controller box and you
were listening, you could probably hear the clicks as those
wheels turned into place. Um and UH. You could even
install multiple drms within a single control box, so you
could have it switch at different times of the day.
(08:04):
So let's say during rush hour traffic you need one
section of the road to be green more often than not.
But then in the middle of the day the traffic
patterns change, so you would want the light behavior to
change as well, and then maybe overnight it changes again. Um.
You could actually do that by having multiple gears in
there and have it switch automatically from one to the
(08:24):
other based upon the time of day. Today, all of
that is kind of it's it's antiquated. I mean, you
don't find that in most systems today because now we
have solid state electronics. Everything's on circuit boards. We don't
have to worry about all those uh those actual mechanical
switches right right, But some of them are still on timers. Yeah,
(08:44):
that's true. That's true. You know when you describe things
that run on gears like that, I'm trying to picture
exactly how this hardware goes together. I can't help singing
Powerhouse in my head when I imagine the gears turning right. Uh.
That okay, so and and Marshall actually wrote a blog
(09:04):
post about this where he links to a video where
you can see. If you want to go to the
to the blogs how Stuff Works and search marshall brains
blog posts, you can find a post that links back
to a video that shows these elements, these mechanical elements. Yep, yep,
I remember that one. Actually I saw that as I
was doing some some research. Um. Now, of course, uh,
(09:27):
you know there are timers, and there are the uh,
the lights that work on a sensor system as well.
Um and the timers seem like they're fairly self explanatory. Yeah,
it's it's a state timer instead of mechanical same same
philosophy as the mechanical ones. But yeah, different different methodology,
but same effect. And that, Um, what happens. You've got
(09:48):
some civil engineers who who observed the traffic patterns, who
come up with the the pattern that should be used
for any particular intersection, the amount of time that each
lane of traffic should have to be able to pass
through that intersection. And um, you know, normally they will
visit an intersection multiple times throughout different days to really
(10:10):
get a good idea of what the traffic patterns are, because,
like I said, they changed throughout the day, right, So
in the evening it may be that, you know, one
particular road is hardly a used all while another one
is is really heavily used. You would want, of course,
the traffic light to favor the heavy use one. Um.
And again this is it sounds kind of simple, except
(10:31):
that when you take into account that you need to
also look at the intersections that are essentially directly adjacent
to that first intersection, like go in in every direction
of that intersection to the next light and see what
that timing is, because that's gonna affect the traffic as well. Well.
Then you have to go one further out from those,
(10:52):
and before long you're looking at a huge net that
incorporates the entire area, which is why it gets so complicated. Um,
but not all of them are timers. Some of them
use sensors, and these are the ones that I find fascinating.
You can you can tell whether or not they have
a sensor generally by looking at the uh not up
(11:13):
where the traffic lights are, but down on the road. Yeah. Um,
there are different kinds of sensors. There are some intersections
they'll use light based sensors like lasers or well, but
but most, in fact, I would I would go so
far as to say the majority of all sensor sensors
used in traffic lights are inductive loop sensors. Yes, that's
(11:34):
the ones that you see, uh, the little grooves in
the pavement directly underneath, like the white stripe where you're
supposed to stop your car generally or or immediately before
in some cases immediately after, which I think is kind
of dangerous if that's the sensor that you're supposed to
be on to trigger the light. But that has to
do with the civil engineers, or perhaps they were painted
(11:54):
by uncivil engineers. Could be UM, but we wonder why
is the Civil War even called that because they were
not UM. So the sensors that are implanted underneath the
roadway act very much like an electromagnet. Yeah, that's essentially
(12:15):
what they are. They You've got a coil of wire
that is underneath the pavement and m and what it's
it's generating a magnetic field and when something really large
and metal passes over it, it acts as an inductor.
And when the system uh can detect that that increase
(12:37):
in the magnetic field. Because once you have the inductor there,
that really boosts the magnetic field. Wants the system detects that,
it's the indicator to say, hey, there's a car waiting
at this intersection, so at the earliest opportunity we should
look at switching the light so that the car can move. Um.
There's some problems with this system though, Yes. The big
(13:00):
this problem being that if you are not in a
fairly you know, like a medium to too larger sized vehicle,
you may not have enough of metal in the mass
of whatever vehicle you're in to to activate the inductor loop.
So what you're saying is, if you were in our writing,
say a motor scooter, motor scooter, bicycle, motorcycle, even even
(13:24):
a small car like a smart car. Smart cars are
tiny and may not even be enough of a mass
in order to get the inductor loop to activate. It
may not generate enough of a magnetic field for the
sensor to be tripped, which means you're sitting at a
traffic light forever waiting for that thing to change, and
it may take until another car or other vehicle pulls
(13:47):
up behind you and perhaps if they're close enough, complete
that that inductor loop so that you can actually trigger
that light. UM and another or of Marshall's brains posts
that that I saw when I was looking at UM
looking at some information for this podcast. UM. Some cities
(14:09):
do have special infrared controllers too for emergency vehicles like
fire engines and police cars, UM, that will allow them
to trip the signals before they get there. It's it's
essentially a remote control of sorts that allow them to
UH to affect the signals and that that keeps them
from having to of course, they're going to go to
(14:30):
the light anyway if they feel like it's safe. But
if they can go ahead and change the traffic lights
rather than having to go through the intersection without affecting
those at all, that that helps them control the flow
of traffic too to some extent. I have a hint
for people who do drive motorcycle, scooters, bicycles, that kind
of thing, if they want to activate those loops. Uh.
(14:52):
This is not the same thing that Chris was just
talking about. Chris was talking about actually changing the light
signals in an official way. Just activating yeah, to let
to let essentially to let the system know, Hey, I'm
here and I would very much like it if I
could get across the street please. Um. What you can
do is you can install a couple of magnets on
(15:12):
the bottom of your vehicle. Uh. And by installed it
just means stick because that's the one thing about magnets.
They stick to metal. Uh some metal, so, yes, well
the metal that you typically find in vehicles. Yes. Uh.
So you get a couple of powerful magnets and you
attach them to the base of the vehicle, and then
when you when you drive over the loop, the magnets
(15:35):
in there, they usually generate a strong enough magnetic field
that that will be enough to trip the sensor and
let it know, hey, there's a vehicle here. So even
if you're just writing in a little scooter that normally
wouldn't activate it, you'll get a signal. Now, these systems
are connected, as we said earlier, to a master control system,
(15:56):
and the master control system's job is to maintain an
on everything that's going on across the the whole uh well,
whatever the area is that it that they oversee, whether
it's a local like thing or a citywide thing, um,
but it usually it monitors traffic twenty four hours a day.
Often these systems can be manipulated remotely so that, let's
(16:19):
say that that the the operator knows there's a fire
uh a fire alarm that's gone off in a building downtown,
and they know where the the fire engine is going
to come from. They can actually proactively uh uh set
up the system so that it stops traffic so that
the fire engine can get through without any dangers of
(16:40):
or reducing danger of collision. I can't ever say without
any because there's always gonna be some something that falls
outside the extremes, right um. And they can also just
keep an eye on how signals are behaving and if
they if there's a signal oiled edge or anything like that,
they can arrange for an electrician in or or you know,
(17:01):
repair unit to go out there and take a look
at it. Um. And they have to consider a lot
of things when they're putting light. As we said, when
they're putting these traffic lights in, it's everything from the
spacing between the traffic signals along the street. Um. They
have to look at the different timing aspects of each
of those. They have to look at just the traffic volume.
(17:21):
How many lanes of traffic are there. Is it going
to to handle the traffic volume well enough so that
you don't have to worry about fiddling with the timer
so much? Um, even the driver behavior on that street.
Because of course, Chris and I know from living in Atlanta,
there are different parts of Atlanta where people drive in
(17:42):
incredibly different ways. Let's say, like to eight five. If
you're not going to eighty miles per hour, you've just
been run over. Now, granted to also does not have
any traffic lights on it, but um, yeah, there's surface streets,
Like there's certain areas of Atlanta where you know, people
drive nice and leisurely and and everyone's kind of you know,
laid back and relax in other parts of Atlanta where
(18:04):
you feel that, you know, you've just entered the road
warrior and two men will enter and one man will leave,
and you know, Mel Gibson's right behind you and burying
it down. And Okay, I've had some really really weird
dreams lately. As all I'm trying to say, I understand
which so yeah, the driver behavior actually does play a
part in how traffic managers look at at setting out
(18:25):
traffic lights and timing them out properly. Um. And it
seems to me that that, um, if you've got lasers
or inductive loops or uh you know, even those rubber
air filled rubbered hoses I guess they're pneumatic hoses of
some kind that uh tell the box that their cars waiting,
it seems like including those would sort of wreck the
(18:46):
plan of trying to manage traffic I mean other than
I mean and by by a master control program. M.
Wait a minute, I'm beginning to understand everything and of line. Um,
but no, yeah, having a master computerized program, uh, it
seems like it wouldn't work. It wouldn't be compatible with
(19:08):
having sensors at individual intersections that allowed cars to trip
the lights as soon as they arrived and we're sitting
there at the stoplight. It seems like it would be
more it's more sort of a if you will, lazy
fair version of traffic. I think they'll make the lights work.
I think part of it. I think part of this
that when that detects that there's a car there, um,
(19:28):
it doesn't necessarily say okay, well we need to change
the lights now. It's it's saying, okay, we need to
change the lights at some point when it's safe to
do so. Keep in mind that if they're steady traffic
going over an intersection, that and that inductor loop, actually
it's picking it up because of course you're still having
cars going through. So these systems are are fairly intelligence
(19:49):
probably the wrong word to use, but they're they're able
to detect traffic at uh if it's if everything's working properly,
they're able to detect traffic and a fairly rely I
will rate. So it's still it's not as planned out
as maybe the timed ones are in the sense of
it doesn't take as much human intervention. But there's still
(20:11):
you know, it's kind of it is kind of adjusting
traffic on the fly. But as I should point out that,
I realized that as soon as you pull up, it
wouldn't necessarily trigger the sensor and automatically turn the light,
because if the box can tell that there are there's
a steady flow of traffic going over the inductors in
the other lanes perpendicular to the ones that you're in, um,
(20:34):
obviously it's not gonna go, oh, well, hey, you know,
I'm just gonna go ahead and stop them. This one
guy really needs to go, so we're gonna stop everybody else.
I sort of always figured that it was a situation
where they go, okay, well it's been ten seconds since
the last car, it's been fifteen seconds since last car.
Traffic is slowing down, there's less of it there. It's
safe to go ahead and give them a yellow light
(20:54):
to prepare them for a red light. And some of
them work on a on a combination of the timer
and the sensor, so some of them have like even
in some cases you'll you'll come up to traffic lights
that you know have the sensors in them, and yet
the traffic lights occasionally change on their own because that
they do ultimately rely on a timer system. Um. And
the anat thing about those timer systems you can actually
(21:16):
program them so that they behave differently on different days
of the year. So if you know, for example, that
say on fourth of July, that a particular stretch of
road is going to be really heavily used, you can
program the system ahead of time to compensate for that
before you know, like you know, back in June you
could you could program it in and then fourth of
(21:37):
July comes around and the system behaves just as you
told it to, so that everything's working properly. Um. Cool, Well,
I'm trafficked out. Well, I think it's a it's one
of those things that we sort of take take for granted.
But the the systems that they've put in to make
this work, um, and try to be sort of intell
(22:00):
gin about the way you manage traffic flow. I mean,
it's obvious anytime there's been a bad storm and the
and the lights are out, how much work actually goes
into planning out the traffic patterns of a city. And uh,
the effect that having those sensors tripping the lights and
and letting the boxes, the controller boxes know what's going
on in an intersection. It's it's obvious how much difference
(22:21):
that makes having that technology available to us, particularly in Atlanta,
where people seem to forget that if the traffic light
is out, you treat it as a four way stop. Yeah, so,
Or when they're flashing yellow on one side and you're
supposed to proceed with caution versus flashing red, which means
you're supposed to come to a complete stop, right and
everybody stops regardless, or if it's flashing yellow, people don't
(22:41):
slow down at all. They're just like that means go,
that means actually go really fast. Yeah, if you're if
you're a starman. Yeah, okay, I've got nothing for that.
If you got that reference right in at tech stuff
at how stuff works dot com, or if you have
any other questions for that matter. But speaking of other questions,
I actually have another listener mail. This listener mail comes
(23:09):
from Trevor, and Trevor says, Hey, Chris and Jonathan, I
just finished listening to your podcast about cyborgs and cybernetics,
and it made me think about a recent book i've read,
Revelation Space by Alistair Reynolds is an excellent example of
advanced cybernetics. UH, pertinent throughout the book. I just thought
I would write and give you that book. Keep up
the good work, Trevor. PS. I know you constantly talk
(23:31):
about virtual environments, but how come I've never heard anything
from you about Second Life. I'm an avid member and
I'm curious why you avoid it. Well, Trevor, it's not
that we're actively avoiding Second Life, at least not more
than anyone else's. UM. Second Life is a virtual environment.
It's kind of think of it like a massively multiplayer
online role playing game without the game. Yes, I mean
(23:53):
you can create games within Second Life, but there's no
game element directly involved. There's no object of winning, there's
nothing like that. It's not you know, but you do
create an avatar and you can wander around a virtual
world and own virtual property and interact with other people
who are also in this world. UM. When it first premiered,
(24:13):
it actually made a big splash. You remember that, like
all the companies that were getting into it. Yes, there
were a lot of companies getting into it. There were
a lot of other organizations trying to uh, trying to
find ways that they could offer their services in the space. Uh.
You know, and I know for a fact that some
libraries were opening virtual reference desks in second life so
that they could, you know, have people come in and
(24:34):
ask them questions. There were bands that would have virtual
concerts and second life. Um. Yeah, you would find things
like I think a lot of news agencies built like
news desks in second life where you could you could
wander into this virtual environment and kind of see what
was going on in the real world. Uh. It was
an idea of like places where people could have virtual meetings,
(24:55):
where you could have maybe a conference online and have
people show up in second life to attend the conference,
and you wouldn't have to leave your home, right. A
lot of interesting ideas. It just never really took off
to the It never lived up to the potential it had. Um,
people still use it, but it's lots and lots and
lots of people still use right, but nowhere near the
(25:17):
number of people that everyone thought was going to use it.
Like a lot of the companies that went in and
spent money developing this stuff have since long since abandoned
those those stations within second life, just because they weren't
you know, it didn't make sense to keep supporting something
that was getting so little traffic. So that's really the
(25:37):
reason why we don't talk about Second Life. It's not
that we have anything personally against it. In fact, I've
written an article about how Second Life works, but it's
just that it really didn't. It doesn't have the impact
that uh, that it potentially could have, and so it
just we just don't end up talking about it. But
(25:57):
if you have any other questions, like I said, tech
Stuff at how stuff rex dot com. And remember we
have an official text stuff Twitter feed now yep, tech
Stuff h s W. Yep, it's all together. So just
go to Twitter and look up tech Stuff h s W.
You'll be able to see our latest tweets, and you
(26:17):
can join our Facebook fan page yep, yep. And again
tex Stuff hs W. You can find us there under
that handle um and uh interact with us a little bit,
you know. When we uh we published some some articles
and things, you can give us some feedback there as well, right, yeah,
and we really do like the audience interaction. It's it's
(26:39):
becoming increasingly more important to us. So please if you
have different ideas, you want to suggest something for the podcast.
Uh you think that maybe, for example, we're talking about
the possibility now, this is a possibility of looking at
h at some point interviewing other people on the podcast
every now and then. If you have ideas of who
(27:01):
we should talk to, give us a shout. Let us know.
Remember we're pretty low on the grand scheme of things.
So if you're saying Steve Jobs, keep dreaming, I want
to interview Benjamin Franklin. Yeah, I had a lot to
do with tech. I'm sending Adele Lovelace. Oh, should be
another good person interview. Yeah, all right, Well that wraps
(27:25):
this discussion up. I hope you enjoyed it, and Chris
and I will talk to you again really soon. If
you're a tech stuff and be sure to check us
out on Twitter Tech Stuff hs wsr handle and you
can also find us on Facebook at Facebook dot com
slash tech Stuff h s W for more on this
(27:46):
and thousands of other topics. Does it how stuff works
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