The Oz of Los Angeles Traffic Lights

How the city controls its traffic system, then and now.

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Reuters

If you think traffic is bad in Los Angeles today, be thankful you weren't around in the early 20th century. Here's what the city's streets looked like back then, via Transportation Issues Daily:

Jon Bruner at Forbes brings us an excellent profile of Edward Yu, the man who makes sure things never look this bad again. Yu is the transportation engineer in charge of setting the timing for the city's several thousand traffic lights. Bruner, who describes Yu as a "soft-spoken engineer with great power," writes:

His department has to take it all in: bikes, trains, big events and, of course, lots and lots of cars. Los Angeles has one of the nation’s worst reputations for automobile congestion, but that’s a simplistic way of looking at things. Its freeways are still the most congested in the nation, but L.A. has 36 times as many miles of surface streets as it does freeways. Those streets, ranging from narrow roads winding around the Hollywood Hills to ten-lane boulevards that cut through canyons of office towers, are heavily traveled - the intersection of Sepulveda Boulevard and Venice Boulevard routinely sees 79,000 cars per day, more than many expressways - but rarely gridlocked.

Most of that power is wielded with the assistance of one of the most sophisticated traffic control systems in the country, the Automated Traffic Surveillance and Control. ATSAC, as it's known, monitors the 4,000 or so intersections across the city. The system collects real-time information on traffic speed, volume and congestion from roughly 18,000 street sensors embedded throughout Los Angeles. Video cameras positioned at hundreds of potential trouble spots allow operators to confirm the cause of any abnormality. 

ATSAC computers continually analyze this data and compare the numbers to historical trends to implement a timing pattern that facilitates traffic at every intersection. In other words, the system is designed not only to fit the city's current travel needs, but also to adapt to its changing ones. Those who want to find traffic patterns before a trip can follow road conditions via ATSAC online. In 2009 Streetfilms gave readers an inside tour of the system that moves Los Angeles:

Traffic signal operation in Los Angeles dates back to 1924, when the city operated 31 Acme traffic signals from a central station - "the first known traffic control center in the world," writes city official John Fisher in a retrospective of the ATSAC system [PDF] in the July 2011 issue of the I.T.E. Journal, a publication of the Institute of Transportation Engineers. That system soon became obsolete, as did another that came along in 1960 (below), found in this slideshow on ATSAC created by Fisher: 

By the 1970s it was clear the city needed a better system to manage its growing traffic problem. In anticipation of the 1984 Olympics it received funding to implement a pilot traffic program in the vicinity of its sports arena, the Coliseum. A month before the games began, the system went online, and it performed well enough to merit citywide expansion.

Over time the system has evolved to incorporate a variety of travel modes. In the early 1990s, after the city's light rail line opened, engineers recognized that even a simple three-car train stopped at a red light blocked an entire stream of car traffic. So ATSAC was adjusted to hold a green signal long enough for trains to pass. Today ATSAC uses this same principle of transit signal priority to facilitate Orange Line bus rapid transit, which has a dedicated busway but occasionally crosses mixed traffic lanes.

ATSAC's success is well documented. A study of the system's performance, published in a 1991 issue of IEEE Transactions on Vehicular Technology, found that ATSAC reduced stops by 35 percent, intersection delays by 20 percent, travel time by 13 percent, fuel consumption by more than 12 percent, and carbon emissions by 10 percent. The cost-benefit ratio was nearly 10 to 1, and the system paid for itself within a single year, according to the report.

Since then the system has swept up a number of awards and been sold to other cities; according to Forbes, it's currently being pitched to Washington, D.C. Still some work remains to be done at home. About five hundred traffic signals in Los Angeles have yet to be incorporated into the ATSAC system, according to John Fisher, though funding has been secured to do that within the next few years.

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