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State DOT is ready to study interstates

PIERRE -- Every 10 years, the state Department of Transportation counts traffic volumes on more than 300 bridges that cross South Dakota's two interstate highways.

Traffic lanes are reduced down to one lane each direction as work is being done on the Highway 281 bridge over Interstate 90 at exit 310 in Aurora County. (Matt Gade / Republic)
Traffic lanes are reduced down to one lane each direction as work is being done on the Highway 281 bridge over Interstate 90 at exit 310 in Aurora County. (Matt Gade / Republic)

PIERRE - Every 10 years, the state Department of Transportation counts traffic volumes on more than 300 bridges that cross South Dakota's two interstate highways.

The latest round of surveys starts this fall. Interchanges will be studied too. DOT staff members then assemble data in a report to be available in 2020.

The report feeds decisions the department weighs as times change.

A bridge necessary 40 years ago might now be questionable if traffic volume has fallen substantially.

Or a bridge might need expansion to match traffic growth.

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For example, repairs are underway at a bridge over I-90 in the Pukwana area, while a bridge over I-29 in Lincoln County structure seems marginal.

Mike Behm, the department's director of planning and engineering, explained the process to the state Transportation Commission last week.

The "vast majority" of South Dakota's interstates were built in the 1960s and 70s, he said.

"Some carry heavy volumes of traffic," Behm said.

Commission member Larry Nelson of Canton asked whether the department kept records of the reasons for bridge locations.

"We don't always know why," Behm replied. He added, "From what we found there is not a document that resides."

Information sometimes was passed down, and sometimes wasn't. The department now is in its fourth or fifth generation of employees since the four-lanes were laid.

"Unfortunately" a checklist wasn't kept, Behm said: "We haven't found that silver bullet of documentation."

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Current employees still ask retired predecessors. "We may be able to find some of that from folks who've been around," Behm said.

Sometimes information comes to light in department records that seem unrelated.

"We'd have to hunt and peck but we may be able to find some of it," Behm said.

The U.S. government commenced the interstate system during the 1950s under President Dwight Eisenhower.

One purpose for the big roads was mass movements of people away from urban areas in case of atomic bombs.

Now motorists look to two lanes or more of one-direction traffic as time savers.

Meanwhile government regulations have multiplied. Mike Vehle of Mitchell, a commission member, said, "We thought it was a daunting task in the 60s? We'd probably be looking at a 30-, 40-year plan (today)."

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