DDI Opening Updates

Traffic Patterns Set to Change in the Coming Weeks as the Exit 16 Diverging Diamond Interchange Opens

Vermont’s first Diverging Diamond Interchange (DDI) at I-89 Exit 16 in Colchester is designed to improve mobility, reduce congestion, and enhance safety for motorists, bicyclists, and pedestrians along the US Routes 2/7 corridor, with traffic scheduled to transition to the new traffic pattern in the coming weeks. Additional updates will be issued as this traffic pattern change approaches.

The new traffic pattern briefly shifts vehicles to the left side of the roadway as they travel through the interchange. This design allows drivers turning left onto interstate entrance ramps to do so without crossing oncoming traffic. Once through the interchange, traffic returns to the normal right side of the roadway. Traffic signals will control both crossover points.

  1. Approach the DDI and choose whether to enter I-89 or continue on U.S. Routes 2/7.
  2. Cross to the left side of the roadway at the first signalized intersection.
  3. Pedestrians and bicyclists use the shared-use path and designated crosswalks to travel safely through the interchange.
  4. Choose your route again, either entering I-89 or continuing on U.S. Routes 2/7.
  5. Cross back to the right side of the roadway at the second signalized intersection.
  6. Drivers exiting I-89 who wish to turn left remain on the left side, allowing for simpler left turns and convenient U-turns to re-enter I-89.

What is a Diverging Diamond Interchange?

A Diverging Diamond Interchange, or DDI, is an innovative, modern interchange design that can relieve traffic congestion and improve safety for drivers, bicyclists, and pedestrians.

Key Benefits

  • Improves safety by reducing conflict points where vehicles can collide.
  • Reduces congestion because left-turning vehicles move more freely.
  • Increases traffic throughput by allowing traffic signals to operate more efficiently and eliminating the need for protected left-turn signal phases.
  • Lowers fuel consumption and delays by reducing time spent waiting at signals.
  • Reduces wrong-way highway entries through the use of raised channelizing islands.
  • Enhances pedestrian and bicycle safety with shorter crossing distances and clearly defined travel paths.

A DDI temporarily shifts traffic to the opposite side of the road so left turns onto interstate ramps can occur without crossing oncoming traffic. This creates a safer, more efficient interchange that moves more vehicles through the area with fewer delays.

Project Phases

The project is being executed in two phases under two separate and sequential construction contracts.

  • Phase 1 – Winter 2023 to Fall 2023: This phase involved utility upgrades and relocations, ledge removal, construction of retaining walls for future pedestrian and bicycle accommodations, and installation of drainage infrastructure. The work was completed by S.D. Ireland Brothers Corporation for approximately $7.5 million.
  • Phase 2 – Summer 2025 to Summer 2027: This phase will focus on roadway construction, including the installation of the DDI, additional turn lanes, and pedestrian and bicycle accommodations. The contract was awarded in May 2025 to S.D. Ireland Brothers Corporation, for approximately $22.5 million.

Phase 2 Schedule

The remaining schedule for Phase 2:

  • Early-mid September 2026 – New Traffic Pattern at Exit 16 Interchange
  • Early October 2026 – Bridge Rehabilitation
  • October 2026 – Construct Concrete Islands and Install Guardrail and Barrier
  • December 2026 – Early Spring 2027 – Winter Shutdown
  • Spring 2027 – Landscaping and Sign Installation, General Clean Up, and Demobilization
  • July 2027 – Project Completion