How do they do that?

A Metro Rapid bus. Photo by Waltrrrr, via Flickr creative commons.

How do they do that? is a new series for The Source that explores the technology that helps keep Metro running and passengers and other commuters moving. Some of it applies directly to the trains, buses and freeways and some of it runs in the background — invisible to nearly everyone but essential to mobility in our region.

How do the street signal lights know to stay green a little longer or turn from red to green a little sooner when Metro Rapid and Metro Orange Line buses are approaching?

The process — called transit priority technology — causes traffic signals to hold green lights longer or shorten red lights to reduce the amount of time buses have to wait at intersections. Buses do still need to stop at red lights, just fewer of them or for shorter time periods.

All Rapid and Orange Line buses are equipped with special transponders that emit signals to a series of wired loops embedded in streets in the city of Los Angeles. As a bus passes from one loop to the next, the data is sent to a centralized computer in downtown L.A. This data is then used to determine the bus speed and location.

Based on the bus speed and location, the data predicts when the bus will arrive at the next signalized intersection and determines whether to extend the green light or shorten the red. All of this occurs in a matter of seconds.

Metro also uses a second transit priority technology — a wireless system — to achieve similar results on some lines or segments of lines that operate outside the city of Los Angeles.

The Metro Rapid Program began in June, 2000. The goal was to improve bus speeds along high-demand and traffic-packed corridors like Wilshire and Ventura boulevards. There currently are 24 Rapid bus lines operating in Los Angeles County.

Have questions for future “How do they do that?” Post them in the comments section below.

6 replies

  1. Great new topic idea!

    My question relates to the light rail synchronization on street running segments. It appears to me that the Blue Line either has priority or street signal synchronization on Washington Blvd to help the train avoid red lights, however, this is not apparent on the Long Beach segment or the Eastside Gold Line. Why is that? Is there anything Metro can do to improve either priority/signal synchronization on the Long Beach – Blue Line segment and Eastside Gold Line? Also, is Metro working to prevent this issue on the Expo Line?

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  2. please answer the 2 ?? above in the previous comments. the orange line stops repeatedly where it should not need to. also what can be done about the long beach section of the blue line?

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  3. The Metro Silver Line needs to have these transponders. In Downtown L.A., the line spends nearly 20-25 minutes stuck in traffic. Please fix!

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  4. A few times each week I pick up somebody on the Orange Line as it comes into the NoHo station. I have watched the bus sit at the light at Tujunga for minutes at a time. In fact, if you stand at the right spot, the light that is west of Tujunga, probably Colfax, can also be seen from the Orange Line station and the bus sits there for long periods of time as well.

    Cross traffic on Tujunga is very light and stopping north/south traffic for 30 seconds every ten minutes during peak hours of Orange Line operation would take many minutes off the end to end commute in the NoHo end of the journey. If the remainder of the route works as ineffectively as this side of the route I would say that your traffic priority technology is anything but a success.

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  5. There are several lights on the Orange Line that almost always catch the bus and some take 1-2 minutes to allow the bus to pass.
    Tujunga,Chandler,Burbank,Van Nuys,Sepulveda,Woodley,Balboa,Reseda,Victory,DeSoto and Canoga almost always the bus will get stuck at the red light.
    The Orange Line needs a “tune-up”.
    And then there is the issue of transponders that don’t work properly, 9201-9218-9222-9489-9492 all have transponder problems that cause those buses to run late and delay service.

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