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.
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