What is the Exit 16 DDI Project?
The project consists of improvements to approximately 1 mile of U.S. Routes 2/7 (U.S. 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 Interstate 89 (I-89) on and off ramps at Exit 16. The project will include improvements to additional intersections along U.S. 2/7 within the project limits. Turning lanes will be constructed along U.S. 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 U.S. 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 U.S. Routes 2/7 (U.S. 2/7) for approximately 1 mile, just beyond the intersection of Sunderland Woods Road at U.S. 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 is available on the Project Overview page.
What are the benefits of the Exit 16 DDI Project?
The Exit 16 DDI Project will improve roadway conditions along U.S. Routes 2/7 (U.S. 2/7) for safety and mobility. The project area extends from the Colchester-Winooski town line north for approximately 1 mile to just beyond the intersection of Sunderland Woods Road at U.S. 2/7. The core of the project is to reconfigure the existing tight diamond interchange at I-89 Exit 16 to a diverging diamond interchange (DDI). Other improvements include:
- Adding turn lanes at the Mountain View Drive, Hercules Drive and Rathe Road intersections,
- Constructing dedicated pedestrian and shared pedestrian/bicycle facilities,
- Modernizing traffic signals at South Park Drive, I-89 Exit 16, Mountain View Drive, Hercules Drive, Rathe Road and at Tigan Street in Winooski City.
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. 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 reduction of conflict points eliminates potential user collisions, thus improving safety and vehicle throughput. With left turn movements operating freely within the DDI, the traffic signals no longer require protected left turn phasing, improving overall traffic operations at the interchange. Additional benefits include reducing driver discomfort, fuel consumption, and lost time. The DDI’s channelizing raised islands significantly reduce the number of wrong-way entrances onto the interstate. The raised islands also create short crossing distances for pedestrians and bicyclists, which increase overall safety forthose users.
In addition to the safety and operational benefits of the DDI, the construction of a DDI is cost effective. The DDI can be constructed utilizing the existing bridge structures eliminating the need to modify or replace them, reducing construction costs. The construction schedule of a DDI is much shorter than the construction of more common interchanges not only reducing overall cost, but also impacts to the traveling public. And the DDI’s compact footprint reduces impacts to the surrounding environment.
Where are DDIs currently in service?
There are 135 DDIs in operation globally, with the first-ever constructed in 2009 in Springfield, Missouri. There are over 110 DDIs in operation, 37 DDIs under construction, and 157 DDIs 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?
Construction of the Exit 16 DDI project will be completed in two phases under two separate construction contracts which will be executed sequentially. The first phase of construction is scheduled to begin in the Winter of 2023 and is anticipated to be completed by the Fall of 2023. The second phase of construction is scheduled to begin in the Fall of 2024 and is anticipated to be completed by the Summer of 2026.
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?
Construction of the Exit 16 DDI project will be completed in two phases under two separate construction contracts which will be executed sequentially. The first phase of construction is scheduled to begin in the Winter of 2023 and is anticipated to be completed by the Fall of 2023. During the first phase, activities will consist mainly of utility relocation, ledge removal, and construction of retaining walls. The second phase of construction is scheduled to begin in the Fall of 2024 and is anticipated to be completed by the Summer of 2026. During the second phase of construction, 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.
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, such as ledge removal with blasting. Attention should be paid through the project limits at all times of the day. During all phases of construction, lane closures and other impacts to traffic should be expected.
What changes can pedestrians, bicyclists, and drivers expect during construction?
Throughout construction, drivers can expect lane closures and other traffic impacts including uneven and unpaved surfaces. Motorists should be aware that short-term Interstate 89 ramp closures may be required depending on construction activities. No detours are anticipated.
During the first year of construction, there will be excavation under the bridges and the construction of retaining walls to allow for temporary pedestrian accommodations along U.S. 2/7 through the interchange. Cyclists can continue to navigate the area as a vehicle like the current condition; however, it is recommended that they dismount and use the temporary pedestrian route.
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.
What changes can pedestrians, bicyclists, and drivers expect after project completion?
Once the Exit 16 DDI is constructed, vehicular traffic on U.S. Route 2/7 (U.S. 2/7) will cross over to the left side of U.S. 2/7 guided by the first traffic signal. Motorists on U.S. 2/7 will be able to turn left onto the Interstate 89 on-ramps freely and vehicles continuing straight on U.S. 2/7 will cross back over to the right side of the roadway guided by the second traffic signal. Vehicular traffic traveling along U.S. 2/7 will still have the opportunity to make a free right turn onto the I- 89 on-ramps prior to the first signal, but will be required to yield to pedestrians, cyclists and other vehicles entering the on-ramp.
Vehicular traffic exiting I-89 and turning left onto U.S. 2/7 will have to yield to oncoming traffic on U.S. 2/7, pedestrians, and cyclists. Vehicular traffic exiting I-89 and turning right onto U.S. 2/7 will be guided by a traffic signal.
Pedestrians and cyclists will be accommodated by a shared-use path along either side of U.S. 2/7. Ramps to the shared-use path will be provided just north and south of the interchange to allow cyclists to access the shared-use path from the roadway, if desired. Four-foot shoulders will be provided for cyclists who wish to remain on the roadway. Users will be required to cross the on and off-ramps onto I-89 at designated areas marked by crosswalks. At the unsignalized approaches, the pedestrians and cyclists crossing at the crosswalks will be equipped with rapid rectangular flashing beacons indicating for motorists to yield. At the signalized approaches, the pedestrians and cyclists will have a dedicated crossing time concurrent with motorists traveling along U.S. 2/7.
Sidewalks will be extended to the south to the project extents at South Park Drive and to the north to Mountain View Drive. Marked shoulders will be provided throughout the project from South Park Drive to Sunderland Woods Road.
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 U.S. 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 stay 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.