A Little More Detail About How Detection Sensors Really Work

DIGGING INTO THOSE TRAFFIC SENSORS: A recent column on traffic sensors not detecting a scooter at an intersection really got readers revved up.

David Blacher points out “the triggering of signals with induction loops has nothing to do with weight. Induction loops sense the presence of a vehicle by the change in the flow of electricity in the wires because of the proximity of a metal object. The term ‘induction’ is used because the nearby metal object ‘induces’ an increase or decrease in the electrical flow.”

David goes on, “part of (the scooter driver’s) issue also may be that motor scooters rely on a great deal of plastic for their bodies. Plastic in any amount will not trigger induction loops.”

Point taken — sorry for the shorthand of using weight instead of metal mass.

Steve emails “in Washington state, where I used to live, bicyclists would wait for a full cycle then, looking carefully for a safe opening, ride through the intersection.

“The legal position was that a traffic signal that did not recognize a vehicle was malfunctioning, and a malfunctioning signal is to be treated as an all-way stop. I don’t know if this would work in N.M.”

Considering the words “wait,” “looking carefully” and “safe opening” would have to apply to crossing a busy arterial, that’s a very good question.

Dick Cochran suggests purchasing a magnetic strip sold in the backs of motorcycle magazines, advertised as a large refrigerator magnet on a string to trigger a signal if thrown on the pavement.

And Ann Cole emails that she agrees there’s a “problem with scooter detection at traffic lights. I visited Boulder, Colo., and found that they have a great solution for scooters and bicycles: there’s a special section of the loop that is in the center of each lane, and well marked. If you wait for the light on that spot, you’re detected just like a car. With the many fuel-efficient scooters, bikes and motorcycles in Albuquerque, traffic engineers need to address this problem.”

In fact, Boulder has switched to a laser system at some of its intersections to sense scooters and bicycles instead of traditional loops. That system runs from $15,000 to $25,000 per intersection. Rio Rancho has converted three intersections on Unser to the laser system and plans to use it on new intersection construction as budgets permit.

David Mitchell, director of Bernalillo County’s Operations and Maintenance Department, says the county has camera detection at 24 of its 55 signalized intersections, and that runs around $20,000 per intersection.

The traditional magnetic loops, which the county has at the rest of its intersections and which the city of Albuquerque, which has 600 signalized intersections, uses, run just $2,800 for a small intersection, $9,000 for a large one.

TO BEST ACTIVATE THE SENSOR: Bernalillo County’s Robert Baker says “the sensitivity can be adjusted on any loop, but the best location to position the wheels on a loop is on top of one of the two parallel perimeter cables, which are easily identified on the pavement near the stop bar. They are the two tar-sealed lanes which are usually 6 feet apart and 30 inches in length. A quadrupole loop has three parallel wires typically 3 feet apart, and the center cable is the best location to position the wheels of a bicycle.”

AND THERE’S NO RECORDING GOING ON: Mitchell adds that “another side topic to this is people, having seen those crude black-and-white video images of accidents on the nightly news from other regions, think that anything video automatically has ‘recording storage’ associated with it. … We asked around, and there is no metro entity or the freeway Traffic Management Center that records video anywhere.”

WHY THOSE MEDIANS AREN’T MAINTAINED: After a reader raised the concern last week that the city isn’t cleaning and weeding the medians it spends a lot of money to construct and landscape, City Councilor Isaac Benton called with some financial perspective.

“Our parks maintenance capabilities are really stretched thin — and those are the people who maintain the medians,” he says.

“As nice as they are and as much as everyone loves them, we really don’t have the resources that we should to be able to maintain the parks and medians. That’s part of the reason I’m questioning spending our gross-receipts tax revenues for constructing roadway projects (like the Paseo del Norte/I-25 interchange) or other projects, recreational projects, when we’re so dependent on those gross-receipts taxes for operations.”

BILLBOARD WISDOM: Finally, a reader emails “a friend of mine back East saw a billboard that read: ‘Honk if you love Jesus, text if you want to meet him.’ ”

Assistant editorial page editor D’Val Westphal tackles commuter issues for the Metro area on Mondays and West Siders and Rio Ranchoans on Thursdays. Reach her at 823-3858; road@abqjournal.com; P.O. Drawer J, Albuquerque, NM 87103; or go to ABQjournal.com/traffic to read previous columns and join in the conversation.
— This article appeared on page D1 of the Albuquerque Journal