Rare interchange eyed for Silverthorne to be built in Grand Junction
The diverging diamond interchange (DDI) is an uncommon and potentially confusing design for a highway exit, but state transportation officials say, under the right conditions, it can be the most effective option.
It is the preferred design for the Silverthorne/Interstate 70 interchange, which the Colorado Department of Transportation plans to reconstruct due to frequent backups and safety issues in the area. But officials are first testing the model out in Grand Junction.
A $4 million diverging diamond will be constructed at Exit 26 on I-70 at US 6 and 50 through a partnership between the city of Grand Junction and CDOT, according to a joint statement released last week. It will be the first in Colorado and one of only a handful of diverging diamond interchanges in the United States.
“This is a first-of-a-kind project for us, and we are very excited to implement this DDI in an area where traffic and commerce are growing rapidly,” CDOT engineer Tim Harris stated. “This project represents a successful public-public partnership — and one that capitalizes on efficient and effective use of tax-payers’ dollars.”
A diverging diamond can carry more traffic than other interchange models and, in Silverthorne and Grand Junction at least, is projected to be less expensive to build than more traditional alternatives.
The design eliminates left hand turns by switching the position of the lanes, shifting drivers to the left side of the road through the interchange, giving motorists direct access to a left-hand ramp and removes the need for a traffic light, according to the statement. Drivers continuing through the interchange are then redirected to the right side of the road.
The model has been shown to increase safety, reducing both the number and the severity of collisions. The design greatly decreases the risk of a “t-bone” crash, transportation officials said.
In Silverthorne, the DDI design won support because it does not require the existing bridges that carry I-70 over Highway 6 to be reconstructed, substantially cutting costs.
The interchange project proposed also includes improvements to the westbound on-ramp as well as the intersection at Wildernest, which along with the DDI construction are expected to cost $15-$19.5 million. Other interchange solutions could cost $30-$50 million, officials said at the open house.
Still, the project hasn’t landed state funding yet.
CDOT officials have pressed forward with studies and design plans for the I-70/Silverthorne interchange despite the lack of money, saying projects that are “shovel ready” tend to be first in line for funding when it becomes available.
“We have different funding scenarios that we continue to manipulate,” CDOT engineer Peter Kozinski told the Summit Daily in a previous interview. “We look for projects that are ready to go.”
The interchange was determined to be in need of a makeover due to safety concerns, frequent backups that occur in the area on busy weekends and projected increases in capacity needs over the next two decades.
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