The subtle straightening of Interstate 190 is requiring the tearing down of a hillside just to the west of a to-be-rebuilt Silver Street interchange.
Towering mounds of earth and rock — more than 100,000 cubic yards of it —loom over the existing interchange.
“Once you see that big pile of dirt, it brings to mind just how big of a project this is,” said Aaron Fagerness, design engineer with project architect HDR of Omaha, speaking of the first phase of a $34 million redesign of a major Interstate 90 connector into Rapid City.
And the earthmovers aren’t done yet, as the first phase of the two-year project hits its stride after years of planning by city and state engineers.
“There’s still about 40,000 yards (of dirt) left to get out of there,” said John Gerlach, project engineer with the South Dakota Department of Transportation.
The current stretch of I-190 was built with what Gerlach called a vertical curve, or bend, in one of the bridges. Moving the interchange to the west will straighten the roadway and allow room for the new interchange.
“We took out the hill to allow for the new bridge and the new alignment for I-190”, Gerlach said.
The existing bridges were built in 1958. The traffic on the roadway underneath the new bridges will be controlled by what is known as a single-point urban interchange, meaning there will be a single traffic signal below the bridge. Similar traffic control was installed at the recently rebuilt I-90 Exits 58 (Haines Avenue) and 60 (East North Street), Gerlach said.
The soil being moved is being "stockpiled" for later use in the project, Gerlach said.
The Silver Street interchange provides access to residential neighborhoods to the north, west and east of I-190 as well as to Central High School, the Rushmore Plaza Civic Center and downtown Rapid City.
The initial work of clearing trees, shrubs and old house foundations along Silver Street has been completed, and the southbound on-ramp to the intersection with Omaha Street has been closed.
Once the major earthmoving is completed and a temporary gravel road is built connecting Silver Street with Philadelphia Street, the southbound off-ramp for Silver Street will be closed, Gerlach said.
A temporary pedestrian walkway, marked with bright orange barriers, has been completed to and from the Silver Street/Settlers Creek neighborhood to the bike path and to Rapid City Central High School.
Both northbound and southbound passing lanes, closed since Oct. 13 to allow crews to build crossover lanes, should return to two-lane travel this week.
Four-lane traffic will continue through the winter until March when traffic will shift to the current northbound lanes as construction begins on the new southbound lanes and bridge.
The project also will include new stretches of West Boulevard and West Boulevard North connecting the interchange with residential areas to the northwest and northeast.
A new northbound on-ramp for access to I-90 will be about where the bridges are now and will eliminate the current on-ramp north of Horace Mann Elementary School.
Also to be included are bike paths and pedestrian sidewalks, as well as upgraded storm sewer, sanitary sewer and water mains.
Reede Construction of Aberdeen is the prime contractor on the project. The project cost includes $32.2 million of state DOT funds, with the city of Rapid City chipping in $1.7 million.
The overall project is set for completion by the end of July 2017.