The biggest project yet for the Colorado Department of Transportation (CDOT) was a huge undertaking to reduce vehicle congestion and reconnect communities on a crucial Denver corridor — plus a beautiful new park right above for nearby elementary schoolers.
The $1.2 billion Central 70 Project, completed earlier this year, includes reconstruction of a 10-mile stretch of Interstate 70 (I-70), between Brighton Boulevard and Chambers Road, and replaced an aged viaduct that was originally constructed in 1964.
WSP was the lead design firm for this project, which added a new express lane in each direction, lowered the interstate roadway between Brighton and Colorado boulevards and introduced a four-acre cover park over a portion of the lowered interstate roadway.
“There’s been a lot of economic disparity between the areas south and north of that viaduct,” said Bryce Binney, WSP senior engineering manager and the project’s design phase structures lead. “One of the goals of this project was to reunite these communities.”
Completed earlier this year, the $1.2 billion Central 70 Project, reconstructed a 10-mile stretch of Denver’s Interstate 70, between Brighton Boulevard and Chambers Road.
Restoring Community Connectivity
The Central 70 Project has rehabilitated and improved Colorado’s I-70 corridor, which serves as a key east-west artery for the Denver area. This is a major regional connector to Denver International Airport and encompasses 1,200 businesses and upwards of 200,000 daily travelers.
The project’s design incorporated elements that were identified by both CDOT and the surrounding community. These included maintaining the safety by eliminating the aging viaduct, adding I-70 capacity and updating the roadway to current highway safety standards.
One key goal was to restore connectivity throughout the community, as the old viaduct presented both a visual and practical barrier that limited opportunities for safe pedestrian crossings. This was accomplished by lowering the interstate below grade and constructing the four-acre cover park, as well as various cross street bridges with Americans with Disabilities Act-compliant sidewalks.
Another focus was Swansea Elementary School, which was recognized as the heart of the Globeville, Elyria and Swansea neighborhoods. As such, the school received significant enhancements like building improvements, a new playground, outdoor classrooms, community gardens and a turf athletic field.
But the project’s massive scope naturally led to a number of challenges, particularly when it came to meeting interests of the many stakeholders along the corridor.
“There were a significant number of third parties involved with this project, such as the city and county of Denver, Union Pacific Railroad, BNSF Railway and a number of different utility companies,” said Jason Buechler, WSP vice president and the project’s design manager. “That required diligent engagement between our team and these stakeholders, in order to make sure that everyone’s needs were met.”
The Central 70 Project replaced an aged viaduct, shown here during demolition and construction in December 2019. The viaduct was originally built in 1964.
Demolition Risks
Construction required a complex phasing approach to limit impacts to the traveling public and the surrounding neighborhood and businesses.
“Because we had to maintain I-70 traffic on the existing viaduct, we had to phase the construction process, which created a number of challenges,” Binney said.
The most technically challenging aspect of this project was lowering the interstate approximately 60 feet adjacent to the existing I-70 viaduct — which had one of the lowest bridge ratings in the state — while also maintaining local connectivity between the residential communities on either side of the interstate.
To maintain that connectivity, low overhead clearance equipment was used to construct new bridges at grade under the existing viaduct, while also avoiding the existing viaduct foundations. Once these new bridges were constructed, the future westbound lanes of I-70 were then excavated under these structures, and then all traffic was shifted off the viaduct and into a temporary head-to-head configuration on the new pavement while the viaduct was demolished.
Demolition of the 2.5-mile viaduct was completed in three months with minimal impacts to the surrounding community, after which the eastbound lanes were excavated and constructed at the viaduct’s previous location.
During demolition, the project team had to avoid damaging the new neighborhood bridges under the viaduct, along with the many residences and businesses standing within inches of the old viaduct.
Another challenge was maintaining operations for three different railroads during the construction of new railroad structures over the interstate, including a bridge immediately adjacent to the busiest railroad yard in the Denver metro area. Completing these new structures while simultaneously accommodating up to 25 daily train crossings required complex construction and phasing.
Lastly, the team had to maintain the lowered I-70 mainline profile above the groundwater table, provide the cover park with amenities and connections to adjacent local streets and the Swansea school, and maintain vertical clearances to bridge crossings and the cover park.
“Denver’s water table in the lowered section was perched on top of bedrock, down about 30 or 40 feet, so depressing the interstate had to be done in view of avoiding that groundwater,” Binney said. “We were able avoid that by reducing the new bridge superstructure depths that were over the ditch that was dug for construction.”
The most technically challenging aspect of this project was lowering the interstate approximately 60 feet adjacent to the existing I-70 viaduct.
Building a Park on a Bridge
The new cover park that connects the Elyria and Swansea neighborhoods spans four acres between Columbine and Clayton streets — the equivalent to more than three football fields.
The park’s events lawn can accommodate 1,450 people and features an array of children’s amenities, including two soccer fields for school hours at the elementary school. There’s an amphitheater, splash pad and 1,500 square feet of playground space, complete with seat walls for more comfortable parental supervision.
“When you’re putting a park on a bridge that’s more or less 1,000 feet wide, and with live plants, that requires a significant amount of drainage,” Buechler said. “That’s why we needed to come up with innovative drainage solutions, in addition to coordinating with the WSP Fire Life Safety team to accommodate a sprinkler system.”
The new four-acre park that connects two neighborhoods features an array of children’s amenities, including two soccer fields.
This park also incorporated numerous aesthetic components to represent the character of the neighborhood, with community-selected art patterns on the retaining and sound walls, along with coloring and monuments on bridges and other community-selected public artwork.
The park required close coordination among a wide range of different teams, but the result is a state-of-the-art green space that will bring the community together for years to come.
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