History of Traffic

Seriously supergood article on the history and technology of traffic here, at Cabinet magazine. How it works, what the terminology means, and how it's (not) controlled. Don't hate me for quoting so much, but it's a really wonderful piece:

In 1930, Philadelphia put the "master controller" (both a device and a person) of its flexible-progressive signal system in the basement of its City Hall; and the groundbreaking Automated Traffic Surveillance and Control (ATSAC) center, created for traffic management during the 1984 Olympics, operates four floors below City Hall in Los Angeles.



Once envied for its vast, efficient freeway system, Los Angeles eventually became the smoggy symbol of destructive automobile dependence and gridlock. Both images, however, are outdated. With one of the earliest and now most extensive traffic management systems, L.A. has become paradigmatic for "intelligent" urban traffic control worldwide. The Los Angeles district of the California Department of Transportation (CALTRANS) operates a traffic management center (TMC) in a fortified building, blocks away from the ATSAC center. ATSAC & CALTRANS combine with the Los Angeles County Public Works TMC to handle traffic flow throughout the region.



Examining Los Angeles further as a case study in both traffic and traffic management, we find a feedback loop between the environment and the system: the environment can be described as the collective movement of vehicles across the urban grid; the system is the infrastructure designed to measure, monitor, and control the environment. More specifically, the system in Los Angeles has two primary realms: the physical and the virtual.



In the physical realm, over 50,000 buried loop detectors, the insulated wire loops that passively detect subtle magnetic field changes from vehicles, combine with over 700 weatherproofed video cameras, some of which are remotely controlled to pan and zoom, to monitor and control traffic flow. Loops automatically trigger software in switching boxes linked to intersection signals but also send data to TMCs that allow traffic engineers to monitor flow patterns and adjust timings remotely. A simple click of a mouse button can start or stop the flow of movement on the grid.



[snips]



When traffic incidents occur, the system acknowledges and responds in various ways depending on the technological level of the area's infrastructure. In the case of most freeways or major intersections in the city itself, cameras are the first observers, recording the collision or obstruction and the immediate effect on the surrounding flow. An extreme incident is known as a Sig-Alert and is defined by the California Highway Patrol as "any unplanned event that causes the closing of one lane of traffic for 30 minutes or more, as opposed to a planned event like road construction, which is planned separately," and is named after Loyd C. "Sig" Sigmon. Mr. Sigmon developed a customized radio receiver and tape recorder that would detect a particular tone and record the bulletin, providing radio announcers with an analogue database of recent traffic incidents. This relieved dispatch from answering phone calls from the press. The first use of this device was in 1955 when doctors and nurses were requested to respond to a train derailment outside the Los Angeles Union Station. A traffic jam was the unintended result. It's oddly appropriate that Mr. Sigmon was to pass away only days before President Reaganís postmortem journey from a Santa Monica funeral home to Simi Valley, north of Los Angeles, shutting down miles of the busiest stretch of freeway in the country (the 405), causing multiple Sig-Alerts in surrounding areas.

Via Urban Cartography