Laser beams will scan thousands of miles of streets in Minneapolis this fall, searching for flaws.

Once the purview of interns and city employees on foot, a van packed with high-tech sensors is taking over the crucial job of measuring the condition of city streets this year. That inspection, performed annually by governments across the state, helps track which roads are most in need of repair.

“It will give us better information than we had before,” said Joe Casey with Minneapolis Public Works. “Also, we don’t have any interns out in the street in traffic. This is safer.”

The Minnesota Department of Transportation and Hennepin County both already use special vans to measure road conditions, but cities are now switching to the technology. St. Paul still checks its streets manually, but Mankato public works chief Jeff Johnson said they switched to a van two years ago.

Johnson, who is president of the City Engineers Association of Minnesota, did not know how many of his members use the service. But he said he assumes it’s on the uptick.

“When we started we had a hard time finding a contractor to perform the work,” Johnson wrote in an e-mail. “Now we have a few contacting us [to] see if we need the service.”

Minneapolis is paying Dynatest, a consulting firm, about $300,000 to drive a specially equipped Mercedes van over more than 1,500 miles of city streets and alleys — they hope to be completed by the first snow. The city expects to repeat the process every three to four years.

The front end of the van is packed with six lasers and two accelerometers, which analyze the ruts and roughness of the road. The back end uses what’s known as a “laser crack measuring system” to capture 3-D images of the cracks in the street, measuring them to the closest millimeter.

The technology could have additional applications in the future. Researchers in the United Kingdom are working with Dynatest data to try to detect potholes before they form, according to the Atlantic’s CityLab.

Engineers focus on different things, depending on the roadway. Dave Janisch, pavement management engineer with MnDOT, said MnDOT is more focused on the roughness of a road — instead of cracks, which preoccupy city engineers — because it is very noticeable at highway speeds.

“We use the roughness index primarily to tell us when a road needs to be fixed,” Janisch said. “And then we use the … type of cracks and the severity and the quantity to tell us what kind of fix to do.”

MnDOT drives its special vans over all state highways and a quarter of county roads every year.

Cities use the cracking information to develop the Pavement Condition Index (PCI), a standard measurement for roads. Under a manual system, inspectors tally the PCI by marking different types of road problems — from cross-hatched “alligator” cracks to cracks running lengthwise or horizontal.

The new automated measuring will also give a “ride value,” illustrating what the road feels like to drive on.

For Minneapolis, determining road conditions is particularly important now, since the city is embarking on a 20-year plan to dramatically boost road reconstruction and repairs.

 

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