BOULDER — Construction crews are close to putting the finishing touches on an unconventional traffic scheme at U.S. 36 and McCaslin Boulevard, which they say will improve flow and safety in the area for cars, bikes and buses alike.
The “Diverging Diamond Interchange” — of which there are just 34 in the country, and two in Colorado — features a funky configuration designed to accommodate 20 years of population growth, without having to widen the bridge at McCaslin.
It’ll be completely finished, the Colorado Department of Transportation says, by the start of 2016, as will the rest of the highway currently held hostage by barriers, cones and uneven road — including the stretch that extends to the Table Mesa exit in Boulder.
But, as U.S. 36 drivers know well at this point, progress usually requires closures.
In the case of the Diverging Diamond project, occasional nightly closures have been the norm since 2014, but from Friday through Oct. 19, there will be a full, four-day shutdown of McCaslin over U.S. 36.
During the closure, eastbound and westbound on- and off-ramps from the highway will remain open, but with right-turn access only. CDOT is encouraging drivers to use Cherryvale Road, 88th Street or Interlocken Loop instead.
Planners from Superior and Louisville, the two towns connected by McCaslin, hope the pain will be worth it.
Since 2002, they have been eying a way to offer extra carrying capacity to meet existing and future traffic needs, but had long been at an impasse.
“We developed this plan to improve the interchange, and we had put a loop in the southwest corner,” said Alex Ariniello, Superior Public Works and Utilities director. “The ultimate plan was to put a loop in the northeast corner, too, but Louisville didn’t want that.”
About five years ago, the Diverging Diamond idea was floated, with the support of CDOT.
“The previous agreed-to solution was going to cost between $20 and $25 million to accommodate the 20-year traffic forecast,” said Troy Ross, Louisville director of Planning and Building Safety. “We did an alternative analysis, and the (Diverging Diamond) rose to the top as being able to handle that 20-year demand, but with the cost brought down pretty much in half.”
So, with a price tag of $12 million — covered equally by the two towns — construction began in 2014.
When the entire project wraps later this year, all left-turns, which planners say are a typical challenge with standard four-way interchanges, will be eliminated. Planners project this could reduce accidents by 30 percent.
Planners say that pedestrian crossings will be shorter and wrong-way entry to ramps will no longer be possible.
The project was designed to not widen the bridge, but instead make space for a pedestrian center walkway and bike lanes.
Regional Transportation District buses will have a dedicated ramp, and will not have to interact with traffic.
