Associated Traffic Engineer Peter Mackprang stands on the corner of 8th and Holly Street in Medford. Mail Tribune Photo / Jamie Lusch - Jamie Lusch

The speed of light

Sitting there at a red light in a busy Medford intersection, how long would you say it takes to cycle through all the red, amber, green and left-turn lights till it gets back around to your turn?

Four minutes? Five? Ten on a bad day, when you're late for work? The answer, believe it or not, is the whole cycle is nearly always under two minutes.

Peter Mackprang knows this. As a city traffic engineer, he monitors Medford's 107 traffic signals from a trailer behind City Hall. Based on traffic counts and citizen information, Mackprang tweaks signals with one goal in mind: to reduce time wasted by motorists sitting at signals.

"I create time — or at least give time back to commuters," he says. "I can't imagine a better job. I'd rather have the challenge of problems that are not easily solved. I get signals to do what people want them to do. It also reduces accidents."

It's not rocket science but it might be the next category below it.

Traffic light timing is based on a "time-space diagram" that factors in travel speeds, volume, distance between intersections and — the wild card — pedestrians crossing the intersection, which can make dozens of vehicles wait and throw off the rhythm of the street for 15 to 30 minutes, Mackprang says.

Because streets in Medford's central corridor always have lots of cars and pedestrians, signals there are set with fixed timings that automatically let people walk across. Away from the city center, Mackprang introduces flexibility with pedestrian-activated buttons and cycles that get triggered when drivers pass over a metal-sensing wire loop embedded in the road (those dark circles and lines you see near intersections).

Signals from these intersections showing activity are sent to Mackprang's computer screen. If he needs to tweak something, he can send commands from his computer to the suitcase-sized control cabinet at the intersection.

"If it's only you at that intersection, you get the minimum time (sitting there), but if there are 10 cars, you get the maximum time, maybe only enough to allow eight vehicles through, so you might have to wait."

Mackprang and others go out in the field to manually count traffic. These numbers, says Mackprang's boss, transportation manager Alex Georgevitch, become the basis for a "very accurate timing plan, very accurate, that is, until a pedestrian introduces complexity. We don't plan for them every cycle or we would lose capacity and everything starts to break down."

The same thing happens when an emergency vehicle preempts the intersection.

A lot of motorists assume traffic signal timings were set in 1953 and haven't been changed since — and that calling public works with a complaint won't do any good, says Georgevitch.

But the fact is, all city employees are tasked to watch for any glitchy signals and public works welcomes input from motorists so they can tweak out every little bug, says Mackprang. (Motorists noticing problems with signals can call 774-2100).

He points to the intersection of Crater Lake Avenue and Delta Waters Road, where unnecessary delays had been going on for years, but with study and engineering, "we're now saving the public about three hours a day, combined — and that's a lot of saved time."

When Mackprang drives through the city of Medford, it looks very different to him than it does to the average resident. He's listening to the signals and they're talking in the language he taught them.

It's a language that's not just numbers and engineering, but one that has to factor in human psychology, says Georgevitch. "All our science is based on the reactions and tolerance of people and trying to quantify that into seconds."

Says Mackprang, "It takes as much background in psychology as engineering. You have to put yourself in the motorist's seat and, using signs and signals, you figure out how to get (signals) to do what you want at the time you want."

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