Viaduct replacement project takes first public step forward

Don’t look for the downtown viaducts to be replaced any time soon, but the chance to weigh in on how it could happen starts this week.

A project to replace the 10th and 11th street three-lane roads running through downtown Sioux Falls and over rail lines will have its first of multiple opportunities for public input from 5 to 7 p.m. Tuesday at Monick Yards, 605 E. Eighth St.

It’s a collaborative process among multiple entities: the city of Sioux Falls and the South Dakota Department of Transportation, in conjunction with the South Eastern Council of Governments/Sioux Falls Metropolitan Planning Organization and Federal Highway Administration.

The public open house is the first step in a major investment study for replacing the viaduct structures. The actual project currently is scheduled in two phases, beginning with 10th Street in 2032 and followed by 11th Street in 2036.

“It typically takes anywhere from six to 10 years once you start with the corridor study to (arrive at) actual construction,” said Shannon Ausen, engineering program manager with the city.

“For us, it doesn’t seem like we’re starting that far out because there are a lot of environmental issues to get through with the actual design.”

The 10th Street viaduct dates back to 1930, the shorter 10th Street bridge over the Big Sioux River was built in 1934, and the 11th Street viaduct was built in 1971. The roadways are the final piece of an agreement from the mid-2000s between the city and state to transition maintenance of state highways within city limits to the city of Sioux Falls.

“We wanted to make sure we timed it appropriately to make sure those bridges still had useful life left, and we’ve done maintenance, and they’ve held up really well, so it’s just time to be taken off the DOT’s inventory and turned over the city,” Ausen said.

The first part of the major investment study is anticipated to include three main phases and take about 18 months. Phase one includes baseline conditions analysis, visioning and identifying transportation-related issues and needs. Phase two includes concept development for the viaduct structures and surrounding local street network. And phase three includes refining phase two concepts to build alternatives, evaluating those build alternatives and developing recommendations.

The study follows a traffic impact study that already has been completed by the city. It concluded that three lanes will continue to be needed in each direction to meet the public’s request for east-west routes throughout the city, Ausen said.

The opportunity to redesign the structures, though, allows the project team to consider “how do we calm that traffic to make it a better neighbor going through downtown,” she said.

“What we’ve heard as we’ve talked about the viaducts with groups downtown is ‘Why are they so high?’ and ‘The pedestrian bridge is narrow. Can we widen it?’ ‘Is there a better way to bring the elevation down to allow better access to the east and west banks of the Big Sioux River?’ When these were built close to 80, 90 years ago, these things weren’t top of people’s agendas at the time.”

The project still calls for two bridges with pedestrian access, but there are alternative for how they’re aligned. One shows two structures similar in alignment to the current situation.

The other shows them aligned more to the north, bringing eastbound and westbound lanes together and tying into Second Avenue at a single intersection before splitting back to the one-way pair west of Second Avenue.

“We still have rail, so we have to make sure we meet their needs and have a safe crossing,” Ausen added.

The project will require an environmental process before it’s cleared to move forward, including evaluating contamination and how the design will deal with rail lines, the flood plain and the Big Sioux River.

“There’s a lot of environmental things, and we have to take our time to make sure we minimize those impacts,” Ausen said.

The process also is moving forward in parallel with the city’s evaluation of the proposed Riverline District, which sits just east of the 11th Street viaduct and is proposed as a potential convention center site.

Those groups interested in downtown development are among the stakeholders the project team wants to hear from before moving ahead, Ausen said.

“And we want to hear from people that work downtown and that live elsewhere in the city,” she added. “We want to hear from them because they travel across the viaducts every day, and we want to hear from people who live downtown and may not travel the viaducts every day but want to get to the east bank of downtown more easily.”

The city has heard “a lot of positive comments on the Sixth Street enhancements,” she added. “So there’s a lot of momentum and excitement for opening up the greenway, and anything we can do to enhance the east and west bank is a win-win.”

Ausen said there should be clarity around the proposed design for the viaducts by some time next year. Additional public meetings are planned for the spring, when initial concepts will be shared, and the fall, when build alternatives and recommendations will be presented.

Written comments will be accepted at the open house and through the study websiteuntil Dec. 20.

This week’s event “is the introductory open house, and this is where people can make sure they get their voices heard,” Ausen said. “We do want to make sure we make it a better neighbor going through downtown. … Those are enhancements we can do, and I know we can find a solution.”