Denver's design shows the new bridge, in green, with a traditional diamond-type interchange on I-70 and a set of braided ramps, in purple, on the west side connecting to I-270.

By Kevin Flynn
Inside-Lane.com

Where jetliners used to cross Interstate 70, Denver soon will be building a new $50.6 million interchange project that will reunite the south side of the old Stapleton airfield with the north side.

But this time, it’s not 747s or DC-10s that will go over top of I-70 traffic, but Stapleton neighborhood residents, regional shoppers and other highway travelers.

The new interchange will carry the Stapleton neighborhood’s Central Park Boulevard over I-70 to Northfield Boulevard in the growing commercial area where Stapleton’s two old north-south runways used to be.

The project is being done by SEMA Construction and Wilson and Company under a design-build contract with Denver. In January, SEMA was given the Notice to Proceed, and the design phase is at 40 percent completion, according to Steven Coggins, Denver’s project manager. Construction is expected to start in June with completion anticipated by October 2011.

A TWA jet is on take-off from Stapleton's old Runway 35 crossing I-70. Several years later, a second north-south runway was added north of I-70 and a second tunnel-bridge was built next to this one for the access taxiway. Photo at Matt Salek's Milepost 61 blog.

The project is using a mix of funding sources including the city’s Better Denver bond program, which is providing up to $30 million.

It is also using $12 million in federal stimulus funds through the American Recovery and Reinvestment Act competitive grants program, channeled through the Denver Regional Council of Governments; and $8 million in other federal transportation funding.

And this week, the Colorado Transportation Commission is expected to approve an application for $1 million in earmarked Interstate Maintenance funds from the Federal Highway Administration to add the replacement of 800 feet of dilapidated concrete on the ramp from westbound I-70 to Interstate 270 to the project. The new ramps tied into this segment but initially it was going to be left as-is.

The Colorado Department of Transportation, which controls I-70, is providing oversight.

Rendering from Denver's interchange study shows the conceptual layout of the wide bridge planned for Central Park Boulevard over I-70. Ramps from and to I-270 straddle I-70 under the bridge.

The “spaghetti” of ramps will allow drivers direct access into both sides of Stapleton via a new Central Park Boulevard bridge, which will cross I-70 just to the east of the existing airport cargo bridge. That is the only bridge over the highway left from Stapleton’s airport days, but it was not adequate for re-use. Central Park Boulevard’s bridge will be between the cargo bridge and the spot where old Runway 17R-35L used to cross over on a long bridge that formed a tunnel carrying I-70. Just to the east of that spot, there used to be a second I-70 tunnel over which a taxiway to Runway 17L-35R was located.

While development of the Stapleton neighborhood has pretty much erased traces of the old runways south of I-70, there are still vestiges of them remaining on the north side.

The Stapleton developer, Forest City Enterprises, will spend an additional amount up to $20 million to construct the extension of Central Park Boulevard from 36th Avenue to Northfield Boulevard.

The design includes two “braided” style ramps, which allow traffic to and from I-270 to cross over entrance and exit ramps from I-70 to Central Park Boulevard. Braided ramps lift one flow of traffic over another to let them change sides without conflict.

While more expensive to build, braided ramps are much safer than old-style “weave lanes” in which traffic trying to merge left onto a freeway had to compete with traffic merging right to get off. Recently constructed examples are at southbound Interstate 25 and Speer Boulevard, and northbound I-25 at Belleview Avenue/Interstate 225.

Old CDOT photo shows then-new I-70 tunnel going under Stapleton Airport's Runway 17-35. Later, a second tunnel was built for the highway, closer to front of photo, for a taxiway to a new runway on the north airfield.