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