Ask MRN: What are these squares in the middle of our roads?

As I travel along streets and highways, I see these squares in the middle of the road. They always are the same size. They have nothing to do with filling a crack or a hole. What are these squares? Do they have something to do with aerial photo calibration? Maybe extraterrestrials left them? 

Jim Frankenhoff, county engineer for the Adams County Highway Department, says those squares are the remains of an adhesive from the material used to hold down traffic counters.

“The counter is an aluminum encased battery powered computer,” he said. “The counter is wrapped in plastic and placed on the pavement. Adhesive-backed nylon mesh, the size of the rectangle, is placed over the counter and pressed on the pavement.  To retrieve the counter, the nylon is usually cut around the counter.  What remains is the outline of the counter. The counter is unwrapped and downloaded.”

Frankenhoff said the counters can count the number of vehicles passing over them. They also give a “relatively good idea” of the type of vehicle — whether it’s a car, tandem axle or delivery type truck, or a tractor/trailer combination.

“(The squares) are all over,” he said. “There also may be multiples at the same location if the road has not been resurfaced recently.”

IDOT does the traffic counts for its average daily traffic maps. Frankenhoff said he doesn’t know the frequency of the state counts, what triggers an update or how the locations are chosen for traffic counters.

“We use the same type of counter to count vehicles and type on roads we may be resurfacing, just to verify IDOT information,” Frankenhoff said.

He said the Adams County Highway Department has two of the computerized counters. They generally run for about three days. They typically are used during the middle of the week to get “normal” traffic counts instead of weekend traffic or holiday traffic figures.

These battery-powered computer counters have replaced the tube counters that were used across roads when, as Frankenhoff said, “us upper middle-aged people were learning how to drive.”

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