Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff.
Speaker 1: Lauren Vogel bomb here in Los Angeles completed a thirty year,
Speaker 1: four hundred million dollar project to synchronize four thousand, five
Speaker 1: hundred traffic lights across the city. By deploying a vast
Speaker 1: network of magnetic sensors installed under roadways plus hundreds of cameras,
Speaker 1: the city can now capture real time traffic data using
Speaker 1: a centralized computer system to synchronize green lights in order
Speaker 1: to reduce LA's notorious congestion and rush hour gridlock. Soon
Speaker 1: after the Los Angeles system was completed, city engineers cheerfully
Speaker 1: reported that the average speed of traffic was up sixteen
Speaker 1: percent and that the time it took to drive five
Speaker 1: miles that's about eight kilometers on l A city streets
Speaker 1: was down from twenty minutes to seventeen point two minutes.
Speaker 1: And yet in l A still held the number one
Speaker 1: spot for most traffic congested city in the United States.
Speaker 1: So why didn't sinking the lights make more a dent
Speaker 1: in the congestion problem? We spoke with Tim Lomax, a
Speaker 1: research fellow with the Texas and m Transportation Institute and
Speaker 1: a thirty five year veteran of traffic analysis. He says
Speaker 1: that adaptive traffic signals are absolutely a good thing, but
Speaker 1: they are not the quick, fixed panacea that frustrated commuters
Speaker 1: believe them to be. Sinct traffic signals work best when
Speaker 1: there is a clear and predictable flow of traffic in
Speaker 1: one direction, explains lomax. I. Think of the traditional commuter scenario,
Speaker 1: in which traffic flows primarily from the suburbs into the
Speaker 1: city center in the morning and reverses course in the evening.
Speaker 1: La Max said that in that kind of scenario, it's
Speaker 1: easy to design a fairly well functioning traffic signal system
Speaker 1: because it's clear which side of the road should get
Speaker 1: longer green lights, and those lights can be timed with
Speaker 1: the flow of traffic to keep cars moving. The problem
Speaker 1: is that traffic patterns in the biggest US cities aren't
Speaker 1: so cut and dried. La Max said, if you look
Speaker 1: at the economic landscape now, there are jobs and populations
Speaker 1: spread all over most metropolitan areas, and the highest volume
Speaker 1: of geting could be from one suburb to another suburb.
Speaker 1: All of your critical bottleneck intersections have heavy traffic coming
Speaker 1: at them in both directions. So how does traffic signal
Speaker 1: sinking work in the first place. A California's city of
Speaker 1: Irvine explains the process like this. The city's traffic control
Speaker 1: center calculates the arrival time for a group of cars
Speaker 1: at each intersection, assuming the cars are traveling at a
Speaker 1: certain speed, and then times the traffic signal to turn
Speaker 1: green just as this group will hit the intersection. More
Speaker 1: green time is given to a main street with greater
Speaker 1: traffic volume than a side street with less volume. Synchronized
Speaker 1: traffic lights don't mean that a driver will encounter an
Speaker 1: unending number of green lights as she drives down a
Speaker 1: major road, though. What it means is that all the
Speaker 1: signals on a main road are set to run the
Speaker 1: same cycle length. That is, the time that the signal
Speaker 1: takes to go from green to yellow, to red and
Speaker 1: back to green again. Ideally, the signal would turn green
Speaker 1: again as the next group of cars arrives. Eli's traffic
Speaker 1: system overhaul went further than most others by using cameras
Speaker 1: and sensors to measure traffic flow and make real time
Speaker 1: adjustments to keep traffic moving. Lomax says that poorly timed
Speaker 1: traffic signals can cause significant delays and that cities can
Speaker 1: make big games by updating signal timing every three years
Speaker 1: to adjust for new traffic patterns. You might not completely
Speaker 1: erase the difference between travel times during off hours and
Speaker 1: peak hours, but you might reduce that difference by as
Speaker 1: much as half. But retiming traffic lights costs money and manpower.
Speaker 1: According to Texas A and M Research, cities should expect
Speaker 1: to spend between three thousand, five hundred and four thousand
Speaker 1: dollars per intersection and devote twenty to thirty work hours
Speaker 1: for analyzing and re timing every signal. And jurisdiction issues
Speaker 1: can complicate matters when these aim stretch of road passes
Speaker 1: through different municipalities. What if one city or suburb doesn't
Speaker 1: want to fork over money for the upgrade. That can
Speaker 1: hold up re timing efforts for years. Here in Atlanta,
Speaker 1: the fourth worst traffic city in the United States, the
Speaker 1: last time that traffic lights were all SINCD was in
Speaker 1: the midnight team seventies, when we had traffic lights at
Speaker 1: only three hundred and twenty intersections citywide. As of eleven,
Speaker 1: we had lights at a further nine hundred and forty
Speaker 1: five intersections that were not included in the coordination system.
Speaker 1: Retiming or sinking traffic lights is only one tool in
Speaker 1: the traffic fighting toolbox. Lomax says that another effective strategy
Speaker 1: is to clear away accidents and disabled cars more quickly.
Speaker 1: He says the commuters aren't as miffed by long drive
Speaker 1: times as they are by unpredictable drive times. What really
Speaker 1: stresses people out is when the daily forty five minute
Speaker 1: commute unexpectedly becomes an hour and a half commute, and
Speaker 1: the most common causes of unexpected delays are accidents and
Speaker 1: stalled cars. Oh and one more reason why synchronized traffic
Speaker 1: lights may not help with traffic flow as much as
Speaker 1: we'd like. Once people realize that congestion has improved on
Speaker 1: a street, it encourages them to get in their cars
Speaker 1: and drive on that street, thereby increasing the number of
Speaker 1: cars on the road, which means more traffic. Today's episode
Speaker 1: was written by Dave Ruse and produced by Tyler Clang.
Speaker 1: For more on this and lots of other carefully timed topics,
Speaker 1: visit our home planet, how Stuff Works dot com.