THE CENTER CELEBRATED TRAFFIC LAST March, in an exhibit called Loop Feedback Loop: The Big Picture of Traffic Control in Los Angeles, as part of an ongoing exploration of Los Angeles’ infrastructure. The exhibit included a public presentation one evening by a representative from the City of Los Angeles’ Automated Traffic Surveillance and Control Center (ATSAC), the agency that controls most of the City’s traffic flow, helping to keep the six million registered cars in the county from becoming just a big pile in Diamond Bar. Steve Rostam, the ATSAC engineer in charge of instrumentation and maintenance for the west side of Los Angeles, spoke to a capacity CLUI audience, and wowed the crowd with his intimate, detailed knowledge of how it all works, from the minutest detail such as the frequency of the inductive loops, to how the city’s underground traffic management center is used to control the flow on Oscar Night, when the lines of limos have to arrive with carefully orchestrated precision—(or else!).
The exhibit, produced by the CLUI’s Transportation Systems Program, in association with the Institute for Advanced Architecture, was on view from March 5 to April 4, 2004, at the Center’s exhibit space on the west side of Los Angeles. It featured displays about the hardware and software of the city’s traffic management systems, from the inductive loops embedded in the road surface, to the centralized traffic control rooms.
To keep things moving, the highway and surface street network of Los Angeles has become the most instrumented and managed of any American city. Sensors embedded in the ground and on poles measure rates and volumes, and deliver their data to control centers where it is assembled into a dynamic image of the collective traffic picture. Increasingly automated, signals also flow out from these control rooms, adjusting timings of lights at intersections and freeway metering ramps, dispatching incident response teams, and updating traffic reports, including live maps on the web. These in turn effect the flow, feeding back into the system and changing its form, as indicated by the sensors that send their signals to the control rooms: the loops feeding back to the loops.
Inductive loops are the electronic bedrock of the traffic management system, with more than fifty thousand of them in the metropolitan area. Loops are generally composed of an insulated wire, set into a shallow trough cut into the pavement to form a square or circular “loop” approximately six feet wide. Each loop is usually visibly linked to a connection point at the curb, and then wired to the traffic control system. The magnetic field generated by low voltage running through the loop is altered by large metal objects passing over it, and this disturbance is detected by the loop and registered by the electronics connected to it on the curb. Each vehicle passing over a loop is a click in the system. Complex intersections can have dozens of loops, and major streets and highways are dotted with them. A series of loops can measure the speed at which cars travel, as well as how many are on the road. Intersections can count the cars that line up before automatically triggering the signal.
The basic timing cycle for traffic lights, called the background cycle, is generally determined by the width of the road multiplied by a pedestrian walking time of 3.2 feet per second. If no pedestrians are present, the cycle may be accelerated or reduced. Before the integration of signalized intersections to a central control point, all intersections functioned autonomously, with loop counting circuitry and timers located in a pole box at the base of a traffic signal pole, or in a metal cabinet on the sidewalk. Though most intersections still possess the ability to operate in this manner, they are increasingly becoming connected by phone lines and dedicated copper wire to the computers at traffic management centers. In the City of Los Angeles, 3,000 of the 4,200 signalized intersections in the city are connected to the Automated Traffic Surveillance and Control Center.
Video cameras are increasingly being deployed by traffic managers and are an important element in the feedback loop. Caltrans (the California Department of Transportation) has 350 cameras, of a planned 500, installed at the moment along the freeway system in Los Angeles. The City’s own Department of Transportation started installing them at high points all over the city, including the roof of City Hall and Patriotic Hall, and now has over 250, out of a planned 500, all of which are connected to the traffic control center. Though expensive, at almost $100,000 per installation, cameras provide a real-time image of the roadway, often providing visual evidence of the source of slowing at trouble spots of the area. New software enables cameras to be read by computers, counting cars and calculating flow. In this way, cameras are doing the job of loops, especially on bridges and overpasses where loops are more difficult to install.
Each municipality in the Los Angeles area has a system for controlling its traffic intersections, or allows another regional authority to do so for them. As the circuitry in the control boxes at intersections gets connected to hubs on a network, these systems become controllable from a central point, and can add their data to the big picture of the regional traffic system. Small local city control centers can be as simple as a networked computer workstation. However the larger systems have a Traffic Management Center (TMC), characterized by rows of workstations facing a video wall. There are around a dozen TMCs in the region, operated by cities like Beverly Hills and Pasadena, transportation agencies such as the MTA and LAX, and regional authorities such as Orange County. In Los Angeles, two major TMCs monitor and control the traffic: the City’s ATSAC for streets, and Caltrans’ TMC for highways.
Four levels under City Hall, next to the Emergency Operations Center for the city government, the City Department of Transportation’s Automated Traffic Surveillance and Control Center, ATSAC, was created to manage traffic around the Coliseum during the 1984 Olympics. It has evolved into the centralized control point for the city’s traffic management systems, run by 20 or so engineers, which develop new and innovative software that they apply to their task.
A few blocks from ATSAC, at the California Department of Transportation building at 120 South Spring Street, Caltrans District 7, which manages the highways in Los Angeles and Ventura counties, has their Traffic Management Center. About 20 people work inside it, including dispatchers for freeway service patrols, signal management personnel, highway maintenance, and a few uniformed California Highway Patrol officers, serving primarily as liaisons to the media. Within a year or two this TMC, and the rest of the Art Deco building that houses the District 7 headquarters, will be torn down, as the new Caltrans headquarters a block away is nearing completion. A new 88,000 square foot TMC will be collocated with the CHP’s Los Angeles Communications Center, at another new facility, called the Los Angeles Regional Transportation Management Center, which will be mounted on earthquake shock-absorbing springs, and is under construction in Glendale. The current CHP Los Angeles Communications Center, where among other things all 911 calls made from cell phones in the region are received, is in a highly secure building on Rosewood Boulevard, near Vermont and the 101 Freeway.
The county of Los Angeles is building a traffic management center at the County Department of Public Works headquarters in Alhambra. The 9,000 square foot TMC will be located in an existing annex building on the property, and should open by 2005. It will contain fifteen consoles as well as the requisite video wall, with sixteen 50 inch monitors. The County is responsible for around 2,000 of the 10,000 intersections in Los Angeles County, including around 800 that are in unincorporated county areas. They are currently preparing to connect 750 of these intersections to the new TMC.
Predictable, cyclical events like rush hours, and even traffic surges brought on by large sporting events, can be controlled automatically, however unpredictable, “non-recurrent” events are the main cause of interruptions to normal traffic flow. Incidents and incident response is therefore one of the most important elements of traffic management. This is why the state police (CHP) are involved so heavily in traffic control, with monitors and dispatchers at the Caltrans TMC and at the CHP Communications Center (there are no police at ATSAC). With over ten million people moving on 650 miles of freeway and 6,400 miles of surface streets in the region, incidents include nearly everything imaginable.
Simplified and brief radio traffic reports have long been the primary way in which the picture of traffic flow is distributed to the public, with only a small percentage of drivers responding in a way that helps to alleviate the stress on the system. As the physical landscape of traffic nears complete instrumentation and digitization, the picture of traffic flow can be easily distributed, and the methods for visualizing the picture can be altered by and for specific end users. Real-time, detailed and complete information on traffic, as it relates to the individual driver’s needs, will soon be available on the web, cell phones, and, eventually, onboard navigation systems, completing the informational feedback loop. The big picture will be integrated with the digits that compose it.