Increased traffic will lead to changes for Exits 71 and 73 of I-29, SDDOT says Original

SIOUX FALLS, S.D. (KELO) — A section of Interstate 29 between exits 71 and 73 near Tea and Harrisburg will be changed but just how much could depend on input from a public meeting set for Tuesday.

The South Dakota Department of Transportation is proposing a six-lane project with three lanes in both directions between exits 71 and 73. The SDDOT also wants to overhaul exit 71 with three possibilities:

  • Compressed diamond interchange
  • Single point interchange (SPI)
  • Diverging diamond interchange

Steve Gramm, the SDDOT planning squad leader for the project, said a projected increase traffic is one of the driving forces behind the change.

Chart from the SDDOT.

SDDOT considers the 2020 traffic flow as well as the forecast for 2050. The average daily traffic (ADT) is for both directions.

The 2020 ADT between exits 71 and 73 was 25,000 to 26,000 vehicles, Gramm said.

The forecast for 2050 is 60,000 each day.

The ADT for the section between exits 71 and 68 is forecast to be 51,000 to 52,000. Exit 68 northbound is for Lennox and Parker.

Gramm said the ADT forecasts consider continued growth in Sioux Falls and outlying communities and the commuter and business traffic that follows that growth.

“The commuter patterns, you will see more people moving to the Beresford area and commuting to Sioux Falls,” Gramm said.

The ramp terminal at exit 71 also needs attention.

“The bridge structure there is fairly common to when it was built in the 1960s,” Gramm said. “There is a hump on the bridge that is the high point.”

The hump can cause some sight distance issues for drivers approaching the ramp, especially if traffic is speeding, Gramm said. The hump can make it more difficult for drivers turning off at the ramp, he said.

“That’s part of the reason why the speed lowers at the interchange,” Gramm said.

The terminal also needs a re-vamp because of increased traffic, he said.

The public input at the planned 5:30 to 7 p.m. meeting at the Tea City Hall is important because motorists who regularly use the route can provide firsthand experience, Gramm said.

“Are we missing something?” Gramm said of how the public can be of help.

The SDDOT uses traffic flow, crash data and other data but that may not fully tell a story such as everyone slowing down and paying more attention because they know an area requires more caution, Gramm said. If drivers slow down and are more cautious that could cause fewer crashes, he said. So, the crash numbers won’t necessarily reflect the potential safety issues.

The I-29 project won’t start until 2028.

The SDDOT first needs approval from the federal administration and it must complete a design phase and because the new interchange ideas will take more space, the SDDOT will need to get more land, Gramm said.

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