Diverging Diamond Interchange

The Diverging Diamond Interchange would eliminate left turns at the traffic signals.

COLCHESTER — Construction on the new Diverging Diamond Interchange at Exit 16 in Colchester is set to begin Monday.

Construction activities will occur from 7 a.m. to 7 p.m. the week of Jan. 23-27. Work is anticipated to take place predominantly off the roadway, according to the Vermont Agency of Transportation, though there is the potential for shoulder or lane closures for the installation of construction signage outside of peak hours.

The project will reconfigure the existing tight diamond interchange to a Diverging Diamond Interchange. VTrans says this change will better serve vehicles, bicyclists and pedestrians traveling through the area. It is expected to be completed by summer 2026. 

The current roadway at the Colchester/Winooski town like design causes significant delays and is one of the least safe interchanges in Vermont. Approximately three collisions occur a month, according to an educational video released by VTrans.

In a DDI, traffic crosses to the left side of the roadway, allowing for ease of access to the interstate by eliminating difficult left turns and the traffic signals which currently account for most of the collisions.

With traffic diverted to the left side of the roadway, vehicles making a left onto the interstate entrance ramps do not have to cross oncoming traffic, creating fewer conflict points.

The DDI’s raised islands are also expected to reduce the number of wrong-way entrances onto the interstate. The raised islands create short crossing distances, which increase overall safety for non-motorized users such as pedestrians and bicyclists.

This coming week, crews will be installing erosion prevention and sediment controls, and installing construction barrier fencing onsite. This work will take place along U.S. Routes 2 and 7 between South Park Drive and Mountain View Drive. 

This construction is part of Phase 1, which includes utility relocation, waterline replacements, telecom duct bank installation, ledge removal and the construction of retaining walls. Phase 1 is anticipated to be completed by fall 2023.

Phase 2 is anticipated to be completed by summer 2025 and will consist of the bulk of the roadway work including the installation of the DDI, the addition of turning lanes and the implementation of pedestrian and bicycle accommodations.

In addition to the safety and operational benefits of the DDI, the construction of a DDI is cost effective, according to VTrans. The project is estimated to cost approximately $14 million and can be constructed utilizing the existing bridge structures. 

See an interactive map of the project here.

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