CP&Y on Central 70
The Central 70 project is a Public-Private Partnership to reconstruct portions of I-70 connecting downtown Denver, Colorado with the Denver International Airport for the Colorado Department of Transportation (CDOT). The project consists of 12 miles in total, with 10 miles of that being heavy construction limits along Central 70 and two miles (one mile on either end of the project limits) to tie into existing infrastructure.
The work consists of widening Central 70 from Chambers Road to Quebec Street, full reconstruction from Quebec Street to Colorado Boulevard, and lowering of the interstate from Colorado Boulevard to Brighton Boulevard. The project also includes the construction of a four-acre cover park over the lowered portion of the interstate and re-striping from Brighton Boulevard to I-25. The final configuration will include four managed lanes in both directions with shoulders for room to eventually expand to six lanes of traffic each way. One lane in each direction will be an Express Lane for toll users and carpoolers or motorcyclists.
As a subconsultant to RS&H, Inc., CP&Y is providing Design-Build Construction Assessment. We are also serving as the Owner’s Representative for CDOT for the entire project. Other team members include the developer, Kiewit Meridiam Partners LLC, who is leading design firm WSP USA (formerly Parsons Brinckerhoff) as well as Roy Jorgensen Associates, Inc., the project operator.
Feature 1 – Cover Park:
A four-acre, 1,007.5-foot-long public cover park will be built over the lowered interstate with water features, playgrounds, an amphitheater, and two soccer fields. One of 22 similar parks in the nation, this feature will connect two Denver neighborhoods that were divided in the 1960s when the original viaduct was constructed. This feature was designed with significant input from the surrounding communities.
Feature 2 – Old Viaduct:
After 57 years, the viaduct of Central 70 has reached the end of its useful life both structurally and in terms of capacity. The viaduct is unable to hold the nearly 200,000 motorists who are using this two-mile stretch of the interstate each day. Removal of the viaduct required slow and careful demolition over a period of roughly five months. Construction crews took measures to prevent and monitor dust, air quality, storm water controls, noise and vibrations caused by the demolition process.
Feature 3 – Lowered Interstate:
The “Mile High Shift” event in May 2021 officially moved all traffic off the old viaduct and onto what will eventually be the new westbound lanes of the lowered section of Central 70. The new interstate profile is 30 feet below ground level, nearly 60 feet below its original elevation as you can see from the picture below.
Lighting: Over 1,700 LED lights will illuminate the eastbound and westbound lanes traveling beneath the cover park. The tunnel also includes 24/7 emergency lighting backed by a large generator.
Fire Protection: Polypropylene fibers serve as passive fire protection in the girders. This is the only instance in which polypropylene fibers have been used strictly as fire protection in the U.S. and possibly the world.
The tunnel also uses a reliable and redundant Fixed Firefighting System (FFFS) controlled by both a Command, Control & Monitoring System (CCMS) and Supervisory Control and Data Acquisition (SCADA).
Additionally, instead of traditional hydrant connections inlayed into precast wall panels spaced alternately on either side of the roadway, the new design uses a dry standpipe system attached to bridge structures. This avoids the need to run pipes 25 feet beneath the frontage road and instead places hydrants along the surface of the frontage road above the tunnel. To address fires within the lowered portion, fire departments attach one pump truck to the hydrant and standpipe above while another truck receives the water in the lowered section. This actually decreases response time by involving two firefighting crews at once.
Drainage: To prevent ponding on the lowered portion of the interstate, impervious layers in the cover park above collect and channel water into pipes leading to a storm water pump station. By rerouting runoff water to the pump station, this design prevents contaminants from seeping into the environment.
Feature 4 – Pump Station:
To remove water from the lowered highway and runoff from surface streets in the area, the Central 70 project includes eight detention ponds and miles of culverts and pipelines, some up to six feet in diameter. This drainage system leads to a pump station especially designed for the Central 70 project to remove contaminants from storm water prior to reintroducing this water to the South Platte River. A robust system, Central 70’s drainage design is capable of handling a 100-year storm event.
Feature 5 – Bridges & Structures:
In addition to four recently constructed bridges within the project limits, the Central 70 project consists of 20 new or replaced bridge structures. There are nine roadway replacements, eight new roadways, two railroad crossings, and the large cover park structure. The railroad bridges carry tracks across Central 70 to and from the largest rail yard in Colorado.
Next Steps & Impact
The design phase Notice to Proceed (NTP) was given in February 2018. Since then, construction has steadily progressed towards the final configuration, which is anticipated to be open to traffic by late 2022. Installation of park elements, landscaping and other punch-list items is anticipated to continue into the following year. Final completion is scheduled for September 2023.
Construction for this project will total $1.2 billion. The subsequent 30-year operations and maintenance agreement will bring the total to $2.2 billion.
The impacts of this project go far beyond reducing congestion and improving safety by expanding upgrading aging infrastructure. The Central 70 project brings thousands of construction jobs to individuals and small businesses with commitments to secure 20% of the project’s hires from the neighborhoods surrounding the project area. On-the-job training is being provided through grant funding. Additionally, the project comes with nearly 150 commitments to the surrounding communities to improve housing, renovate a nearby school, and ensure access to neighborhood sources for food and public transportation among other generous donations. In total, the Central 70 project will provide an estimated $17.8 billion of new economic activity to Denver and the state at large.
For more information about this and other CP&Y transportation projects in Colorado, reach out to Zach Stone, PE by phone at 719.685.8608 or by email at firstname.lastname@example.org. Also available to answer your questions about CP&Y's construction services, Gary Stringer, PE, CFM may be reached at 214.589.6910 or email@example.com.
CP&Y would like to offer a big THANK YOU to the Colorado Department of Transportation for providing much of the invaluable information provided to form this article. You can also click here to visit the Central 70 project website run by CDOT.