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Preface Events Investigation Conclusion

168 Days: In The Beginning: Green, Yellow, Red

By Ken Snyder

Now that I was at new employment "home" I found out that things at BPU were much different than the airline business. Where I had been required to provide my own tools before I was now issued most of the tools I would use everyday -- I still brought in some of my personal tools, especially ones I was really comfortable in using, like terminal crimpers, wrenches and a magnetic-tipped screwdriver with replaceable bits. Because we would be traveling all over the city we had our own work vans. At BPU they had negotiated in their union contract that the shift started at 8:00AM, and lunch was paid time -- I had never started a day shift job that late; at American it was either 7:00AM (8-hour day) or 5:00AM (10-hour day), and lunch was just about always on your own half-hour.

Immediately I was introduced to how traffic signals work. The different directions of travel are called "phases" and there can be more than you think: four primary directions (normally north, south, east, and west), four left-turn directions, each off of a primary direction, and in some cases as many as four more directions. Some intersections have special directional considerations, and there are also pedestrian directions as well. Each intersection (or in some cases, sets of intersections) has a control cabinet housing the components that activate the signals. Inside the cabinet is a controller, a conflict monitor, electrical load switches (as many as 16 in the newest cabinets) that transfer electricity to the signal lights, power switching equipment and (in some cases) traffic detection equipment. There can be other equipment as well, the exact combination of equipment is determined by the Traffic Engineers and the equipment manufacturers.

The controller determines which signal each direction used is getting at any time, and the conflict monitor makes sure that the signals don't give off a potentially dangerous indication: for instance, a northbound green signal and a green signal to a cross-street (eastbound or westbound).

Some signals are just timed in each direction: they stay green one way for a particular amount of time, then change to allow a green signal another way for a particular amount of time. Others use several different methods to detect traffic, from wire loops embedded in the pavement, to cameras pointed at the street looking for a change in the patten they have learned, to wireless detection modules set into the pavement that send signals to a receiver connected to the cabinet.

It's far more than just "green, yellow, red."

Next: Learning The Ropes
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The standard you walk past is the standard you accept.