WEBVTT - Does Syncing Traffic Lights Reduce Traffic?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff.

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<v Speaker 1>Lauren Vogel bomb here in Los Angeles completed a thirty year,

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<v Speaker 1>four hundred million dollar project to synchronize four thousand, five

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<v Speaker 1>hundred traffic lights across the city. By deploying a vast

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<v Speaker 1>network of magnetic sensors installed under roadways plus hundreds of cameras,

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<v Speaker 1>the city can now capture real time traffic data using

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<v Speaker 1>a centralized computer system to synchronize green lights in order

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<v Speaker 1>to reduce LA's notorious congestion and rush hour gridlock. Soon

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<v Speaker 1>after the Los Angeles system was completed, city engineers cheerfully

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<v Speaker 1>reported that the average speed of traffic was up sixteen

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<v Speaker 1>percent and that the time it took to drive five

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<v Speaker 1>miles that's about eight kilometers on l A city streets

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<v Speaker 1>was down from twenty minutes to seventeen point two minutes.

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<v Speaker 1>And yet in l A still held the number one

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<v Speaker 1>spot for most traffic congested city in the United States.

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<v Speaker 1>So why didn't sinking the lights make more a dent

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<v Speaker 1>in the congestion problem? We spoke with Tim Lomax, a

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<v Speaker 1>research fellow with the Texas and m Transportation Institute and

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<v Speaker 1>a thirty five year veteran of traffic analysis. He says

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<v Speaker 1>that adaptive traffic signals are absolutely a good thing, but

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<v Speaker 1>they are not the quick, fixed panacea that frustrated commuters

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<v Speaker 1>believe them to be. Sinct traffic signals work best when

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<v Speaker 1>there is a clear and predictable flow of traffic in

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<v Speaker 1>one direction, explains lomax. I. Think of the traditional commuter scenario,

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<v Speaker 1>in which traffic flows primarily from the suburbs into the

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<v Speaker 1>city center in the morning and reverses course in the evening.

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<v Speaker 1>La Max said that in that kind of scenario, it's

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<v Speaker 1>easy to design a fairly well functioning traffic signal system

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<v Speaker 1>because it's clear which side of the road should get

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<v Speaker 1>longer green lights, and those lights can be timed with

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<v Speaker 1>the flow of traffic to keep cars moving. The problem

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<v Speaker 1>is that traffic patterns in the biggest US cities aren't

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<v Speaker 1>so cut and dried. La Max said, if you look

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<v Speaker 1>at the economic landscape now, there are jobs and populations

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<v Speaker 1>spread all over most metropolitan areas, and the highest volume

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<v Speaker 1>of geting could be from one suburb to another suburb.

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<v Speaker 1>All of your critical bottleneck intersections have heavy traffic coming

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<v Speaker 1>at them in both directions. So how does traffic signal

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<v Speaker 1>sinking work in the first place. A California's city of

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<v Speaker 1>Irvine explains the process like this. The city's traffic control

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<v Speaker 1>center calculates the arrival time for a group of cars

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<v Speaker 1>at each intersection, assuming the cars are traveling at a

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<v Speaker 1>certain speed, and then times the traffic signal to turn

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<v Speaker 1>green just as this group will hit the intersection. More

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<v Speaker 1>green time is given to a main street with greater

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<v Speaker 1>traffic volume than a side street with less volume. Synchronized

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<v Speaker 1>traffic lights don't mean that a driver will encounter an

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<v Speaker 1>unending number of green lights as she drives down a

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<v Speaker 1>major road, though. What it means is that all the

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<v Speaker 1>signals on a main road are set to run the

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<v Speaker 1>same cycle length. That is, the time that the signal

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<v Speaker 1>takes to go from green to yellow, to red and

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<v Speaker 1>back to green again. Ideally, the signal would turn green

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<v Speaker 1>again as the next group of cars arrives. Eli's traffic

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<v Speaker 1>system overhaul went further than most others by using cameras

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<v Speaker 1>and sensors to measure traffic flow and make real time

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<v Speaker 1>adjustments to keep traffic moving. Lomax says that poorly timed

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<v Speaker 1>traffic signals can cause significant delays and that cities can

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<v Speaker 1>make big games by updating signal timing every three years

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<v Speaker 1>to adjust for new traffic patterns. You might not completely

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<v Speaker 1>erase the difference between travel times during off hours and

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<v Speaker 1>peak hours, but you might reduce that difference by as

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<v Speaker 1>much as half. But retiming traffic lights costs money and manpower.

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<v Speaker 1>According to Texas A and M Research, cities should expect

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<v Speaker 1>to spend between three thousand, five hundred and four thousand

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<v Speaker 1>dollars per intersection and devote twenty to thirty work hours

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<v Speaker 1>for analyzing and re timing every signal. And jurisdiction issues

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<v Speaker 1>can complicate matters when these aim stretch of road passes

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<v Speaker 1>through different municipalities. What if one city or suburb doesn't

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<v Speaker 1>want to fork over money for the upgrade. That can

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<v Speaker 1>hold up re timing efforts for years. Here in Atlanta,

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<v Speaker 1>the fourth worst traffic city in the United States, the

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<v Speaker 1>last time that traffic lights were all SINCD was in

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<v Speaker 1>the midnight team seventies, when we had traffic lights at

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<v Speaker 1>only three hundred and twenty intersections citywide. As of eleven,

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<v Speaker 1>we had lights at a further nine hundred and forty

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<v Speaker 1>five intersections that were not included in the coordination system.

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<v Speaker 1>Retiming or sinking traffic lights is only one tool in

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<v Speaker 1>the traffic fighting toolbox. Lomax says that another effective strategy

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<v Speaker 1>is to clear away accidents and disabled cars more quickly.

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<v Speaker 1>He says the commuters aren't as miffed by long drive

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<v Speaker 1>times as they are by unpredictable drive times. What really

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<v Speaker 1>stresses people out is when the daily forty five minute

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<v Speaker 1>commute unexpectedly becomes an hour and a half commute, and

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<v Speaker 1>the most common causes of unexpected delays are accidents and

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<v Speaker 1>stalled cars. Oh and one more reason why synchronized traffic

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<v Speaker 1>lights may not help with traffic flow as much as

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<v Speaker 1>we'd like. Once people realize that congestion has improved on

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<v Speaker 1>a street, it encourages them to get in their cars

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<v Speaker 1>and drive on that street, thereby increasing the number of

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<v Speaker 1>cars on the road, which means more traffic. Today's episode

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<v Speaker 1>was written by Dave Ruse and produced by Tyler Clang.

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<v Speaker 1>For more on this and lots of other carefully timed topics,

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<v Speaker 1>visit our home planet, how Stuff Works dot com.