What is the Exit 16 DDI Project?
The project consists of improvements to approximately 1 mile of US Routes 2/7 in Colchester. The core of the project is the installation of Vermont’s first Diverging Diamond Interchange (DDI) where US Routes 2/7 meet the I-89 on and off ramps at Exit 16. The project will include improvements to additional intersections along US Routes 2/7 within the project limits. Turning lanes will be constructed along US Routes 2/7 at the intersections of Mountain View Drive, Hercules Drive, and Rathe Road. The existing traffic signals will be upgraded at the intersections of Tigan Street, South Park Drive, Mountain View Drive, Hercules Drive, and Rathe Road. Pedestrian and bicycle facilities such as sidewalks and shared-use paths along US Routes 2/7 will also be constructed within the project area.
Where is the Exit 16 DDI Project?
The project area extends from the Colchester-Winooski town line north along US Routes 2/7 for approximately 1 mile, just beyond the intersection of Sunderland Woods Road at US Routes 2/7 in Colchester. The project also includes traffic signal upgrades at Tigan Street in Winooski.
What is a DDI and how does it work?
A Diverging Diamond Interchange (DDI) allows traffic to cross to the left side of the roadway to ease access to the interstate and eliminate difficult left turns without increasing the number of lanes or traffic signals. For more details on DDIs, visit our What is a DDI page. A brief instructional video on the benefits and functionality of the DDI will be available on this website. Check back soon!
What are the benefits of the Exit 16 DDI Project?
The Exit 16 DDI Project will improve roadway conditions along US Routes 2/7 for safety and mobility. The DDI is anticipated to reduce traffic congestion and the number and severity of crashes occurring at the interchange of US Routes 2/7 and Interstate 89. The addition of turning lanes and upgrades to the existing signals at adjacent intersections, and improvements to pedestrian and bicycle facilities throughout the project area will also help mitigate congestion and safety concerns throughout the corridor.
In addition, the DDI design allows for incorporation of the existing Interstate 89 bridges, therefore reducing the project footprint and impacts to adjacent properties. Using the existing infrastructure also dramatically decreases construction costs.
Also, the DDI’s channelizing raised islands significantly reduces the number of wrong-way entrances onto the interstate.
Where are DDIs currently in service?
The are 98 DDIs in operation globally, with the first ever constructed in 2009 in Springfield, Missouri. Currently, 121 DDIs are in advanced design or planning in the United States.
Below, are just a few of the DDIs in the United States. A total of 46 states have DDIs in use or in planning.
Will the DDI cause driver confusion?
No. Roadway elements such as signing, pavement markings and barriers will assist and guide motorists through the interchange properly.
How will motorists and plow drivers travel through a DDI in the winter?
Diverging Diamond Interchanges are being installed all over the US since their conception in the early 2000s. Dozens of snowy states in the US have operational DDIs, including Utah, Colorado, Idaho, Minnesota and Alaska. Here is a great link that discusses the concerns raised and benefits experienced in Michigan (https://www.ohm-advisors.com/insights/michigans-diverging-diamond-interchange-reaps-benefits).
VTrans has coordinated with several of these state DOTs to discuss concerns with winter maintenance of DDIs and found that they aligned with VTrans' current standard winter maintenance activities. VTrans maintenance crews are aware of the Exit 16 DDI project and are prepared to clear the roadways of snow and ice per the Agency's Snow and Ice Control Plan (https://vtrans.vermont.gov/operations/winter-maintenance/faq).
Motorists should practice the same safe winter driving practices on all roads, including following posted roadway signs and traffic signals, keeping a safe distance from snowplows, expecting delays and allowing extra travel time. Additionally, users will be able to rely on a robust signing design and traffic signals to assist in guiding them through the interchange when pavement markings are temporarily covered.
How will the DDI function during a power outage?
The traffic signals will be connected to a back-up natural gas-powered generator; in the event that the generator fails to provide enough power during the outage, motorists should treat the traffic signals as stop signs, per the law.
How long will construction take?
The project is scheduled to be advertised for bid in the Winter of 2022. The contract will be awarded in the Spring of 2022.
How can I learn more about the project?
This website provides an overview of the project and is a one-stop resource for all project related materials. Please visit the Document Library to preview all public outreach and meeting materials.
Prior to construction, public meetings will be held to share project information and provide an opportunity for community discussion. Information on the Exit 16 DDI Project will also be available on VTrans social media accounts including Twitter, Facebook, Instagram, and YouTube. In addition, project news and construction updates will be emailed to those who sign-up for our email distribution list. Please submit your email to be added to the distribution list here.
What can I expect during construction?
During the first construction season, scheduled to begin in the Fall of 2022, activities will consist mainly of utility relocation, ledge removal, and possibly some drainage work. During the second construction season, scheduled to begin in the Spring of 2023, the roadwork will begin including the construction of the DDI, addition of turn lanes at the adjacent intersections, upgrades to the existing traffic signals, and construction of the pedestrian and bicycle accommodations. Lane closures and other impacts to traffic should be expected during both primary construction seasons.
During what hours can we expect construction activities?
Most construction will occur during nighttime hours, 7:00 PM – 6:00 AM. There may be some construction activity outside of the roadway that will be allowed during the day. Attention should be paid through the project limits at all times of day.
Will the I-89 Exit 16 ramps be closed during construction?
Long term ramp closures are not anticipated at this time, but motorists should be aware that short term closures may be required depending on the construction activity.
Will there be detours during construction?
There are no detours anticipated at this time.
Will bicyclist and pedestrians be able to cross through the interchange during construction?
A temporary path designed for pedestrian and bicycle use will be constructed early in the project to minimize pedestrian/bicycle & vehicle conflicts.
How will tractor-trailers and large trucks successfully navigate the new Diverging Diamond Interchange roadway design?
The Exit 16 DDI has been designed for all vehicles legally allowed to operate on Vermont’s roads, including 67-foot tractor-trailer vehicles. All turning movements have been designed to accommodate the rear tire tracking of long vehicles. For on- and off-ramps where the turns are tight, the design includes concrete tracking aprons to allow rear tires to track without damaging the roadway infrastructure or the vehicle. Please refer to the linked image that shows the location of one of the concrete tracking aprons. In addition, vehicle clearance from the proposed paved surface to the bottom of the interstate bridges was evaluated to ensure taller tractor-trailer vehicles can safely clear the structures.
How will the Exit 16 DDI project accommodate heavily left-turning vehicles at Mountain View Drive?
As part of the Exit 16 DDI Project, a new traffic signal system will be installed on US Route 7 at Mountain View Drive. An additional dedicated left-turn lane will be constructed on Lower Mountain View Drive for southbound US Route 7 traffic. The traffic signal timing for these two left-turning lanes will be isolated such that it no longer overlaps with green times for traffic leaving Water Tower Hill on Mountain View Drive. For traffic turning left onto Mountain View Drive, especially during the morning commute hours, additional green time will be added to the traffic signal system to accommodate those drivers. Additionally, the traffic signal systems at all affected intersections will be coordinated with each other.
How can I say informed during construction?
During construction, weekly Construction Updates will be distributed to notify the public of construction activities and travel conditions for the following week. Project Updates and Traffic Alerts will also be issued on an as needed basis throughout the life of the project. All project updates will be posted on this website.
To sign-up to receive project updates, please click here.