Bridge over U.S. 36 to feature 'diverging diamond interchange'

BOULDER COUNTY, Colo. - A bridge that was remodeled in 2005 is about to get another facelift, which will have drivers wondering if they suddenly took a wrong turn to the UK.

On Monday, the Colorado Department of Transportation will begin construction on a diverging diamond interchange on McCaslin Boulevard over U.S. 36 between Louisville and Superior. The interchange will have drivers cross the bridge on the left side of the roadway, similar to driving in the UK.

Watch this animation of a similar design from the Missouri Department of Transportation: https://t.co/EUcSSBf6Ol

"It will provide a lot more of a continuous flow pattern," said CDOT spokeswoman Crystal Morgan.

Using the diverging diamond interchange, drivers will encounter one fewer stoplight. For drivers using the McCaslin Boulevard off-ramp in either direction, instead of waiting at a red light to turn left, they will immediately merge onto the closest lane on the left side of the bridge. They won't hit a stop light until they have crossed the bridge, when the lanes start to go back to the appropriate side of the street.

"If you are travelling northbound on McCaslin, you actually have to stop at two stoplights, sometimes three depending on where you're coming from," said Morgan. "This diverging diamond interchange includes the widening of this bridge (and) will help to alleviate a lot of the congestion that's here now and is going to come in the future."

7NEWS wanted to know why this reconstruction is necessary, especially since the bridge was redone in 2005 for $6 million.

"This is not throwing away the work that was done in 2005, this is adding on to it," said Morgan. "With the growth that is coming to this area, this was never intended as a long term solution."

Creating a diverging diamond interchange is going to cost slightly more than $12 million. The town of Superior is paying more than $5 million, the city of Louisville is paying about $3.5 million, RTD is paying $3.5 million and CDOT is contributing $950,000.

In 2005, federal funds covered $3 million, with the other half split between the city of Louisville and town of Superior.

That project removed a left turn red arrow for drivers traveling southbound on McCaslin Boulevard trying to get onto eastbound U.S. 36 toward Denver. Once construction was complete, those drivers used a right lane entrance that looped on to eastbound U.S. 36. The project was meant to eliminate long traffic backups getting on and off U.S. 36.

"(It) did create a safety hazard," said Morgan. "The bridge will be widened, which is something that they were not able to do in 2005."

The 2005 construction also added a pedestrian bridge over U.S. 36 to a new RTD stop on the south side of U.S. 36.

"Prior to those upgrades this interchange itself was actually a level 'F,'" said Morgan.

The 2005 construction also added a pedestrian bridge over U.S. 36 to a new RTD stop on the south side of U.S. 36.

"About 20 percent of the project in 2005 will be upgraded as a part of this project."

Twenty percent of a $6 million project is being kind of torn up?" asked 7NEWS reporter Marshall Zelinger.

"Torn up, if you will; upgraded. It was never intended as a long term solution," said Morgan. "In 2005, this was an unheard of design concept, especially for Colorado. We're elongating (the bridge's) lifespan for another, at least 20 years."

CDOT is planning public education opportunities, since there is bound to be confusion for an alignment that will have drivers on the opposite side of the road.

"We do anticipate that folks will need some time getting used to this," said Morgan. "We are undertaking a very large outreach effort for the local communities and those driving this interchange daily."

This will be Colorado's second diverging diamond interchange. The first is about to open in Grand Junction.

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