NewsState of Growth


Yes, there is logic behind Colorado Springs' unconventional intersections

They may seem confusing, but they move traffic more efficiently
Yes, there is logic behind Colorado Springs' unconventional intersections
Posted at 5:44 PM, Feb 27, 2021
and last updated 2021-02-27 19:52:59-05

COLORADO SPRINGS — As more people continue to move here, they of course are bringing more traffic with them. It’s led our city’s traffic engineers to come up with some pretty unique roadway designs to accommodate that traffic.

If you take a look at the Facebook comments on News 5’s story about the new diverging diamond interchange planned for Powers Blvd. and Research Parkway, you’ll find plenty of people confused by the design.

One person asked what the science was behind this seemingly over-complicated design.

According to CDOT, “A Diverging Diamond Interchange crosses traffic to the left side of the road across a grade-separated interchange and allows vehicles to have direct access to freeway ramps without having to wait at a traffic signal. Vehicles cross to the opposite side of the road at a traffic signal. Left turns at the interchange do not cross oncoming traffic, which results in fewer crashes because there are fewer potential conflict points.”

Colorado Springs already has one diverging diamond interchange at Fillmore and I-25.

“It just allows your intersections to operate more efficiently,” said Colorado Springs' Head Traffic Engineer Todd Frisbie.

While the Powers and Research interchange is a CDOT project and design, Frisbie is plenty familiar with the diverging diamond interchange design.

“You don’t have to accommodate a left turn phase,” Frisbie said. “To get vehicles through, you basically have a two-phase signal. You go green for one direction, stop it, then you go green for the next direction.”

The design brings more than just shorter wait times.

“Eliminating left turns, which is the source of your more serious crashes, the diverging diamond is actually a safer intersection,” he said.

But how about some of our other intersections that seem complicated for no apparent reason?

At the intersection of Woodmen and Union, you’ll come across what’s known as a 'continuous flow' intersection, built in 2018.

The intersection’s former design would stop traffic in four phases. First, traffic on Woodmen wanting to go straight would have to stop to let Union traffic wanting to go straight cross. Then, it would have to keep waiting while left turning-traffic from Union onto Woodmen crossed. It would have to stay stopped to let left-turning traffic from Woodmen onto Union cross, before finally getting the green light to continue going straight on Woodmen.

“If you can pull a phase out of the intersection, you’re going to make it more efficient,” Frisbie said.

So that’s exactly what they did.

With the new continuous flow design, traffic wanting to turn left from Woodmen onto Union can cross over opposing Woodmen lanes while those lanes are stopped farther down waiting for Union traffic to cross. That way, when the lights turn green for Woodmen traffic to continue straight, left turners can make their protected turn onto Union as well.

“You can kind of move left-turners and move through-traffic at the same time,” Frisbie said.

If you’re a visual person and this still seems confusing, this website devoted to educating people about continuous flow intersections can help you visualize the concept.

The continuous flow design will also extend the life of the intersection at Woodmen and Union.

“It originally was to be a grade-separated intersection,” Frisbie said.

But that would be expensive. He says this design allows the city to increase the intersection’s capacity while saving some money for other projects.

We’re also seeing another unconventional style of intersection on the increase.

“Another example is say a roundabout,” Frisbie said.

In recent years, intersections on Research Pkwy east of Powers Blvd., which might have at one time been built with stop signs or traffic lights, were instead built as roundabouts.

“Traffic engineering… we review all these development plans… we like it when we see roundabouts,” Frisbie said.

Roundabouts bring less maintenance, since they don’t need electricity like signalized intersections. But that’s not all.

“If you reduce conflict points, you can make your intersection safer,” he said. “A traditional four-legged intersection, I think you have 32 conflict points. With a roundabout you have 8.”

So for those wondering, sure, these designs may be unconventional.

“What we’re trying to do, is we’re trying to solve a recurring congestion problem, and we’re trying to utilize our infrastructure in the best possible way,” Frisbie said.

But when you look at the big picture, they don’t seem so complicated after all.

“If we can come up with innovative designs that improve flow, and improve safety, and reduce maintenance costs, I think that’s a good use of our transportation dollars,” he said.