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Greenwich Substation and Line Project

Eversource is constructing new underground transmission lines; modifying the Cos Cob Substation to accommodate the new lines; and constructing the new Greenwich Substation. 


As part of always working to serve you better, Eversource is constructing two, new 115-kilovolt (kV) electric lines and building a new substation to improve reliability in Greenwich, Connecticut.

The new transmission lines will extend 2.3 miles from Eversource’s existing Cos Cob Substation on Sound Shore Drive to the new Greenwich Substation at 290 Railroad Avenue. The lines will run underground, primarily under town streets, including those in Bruce Park.

The project also includes modifications at the Cos Cob Substation located at 12 Sound Shore Drive.

Greenwich project map

Click to enlarge map

Project Facts:

  • Underground route length: 2.3 miles
  • Location: Greenwich, Connecticut
  • Line voltage: 115,000-volt (115-kV) transmission line
  • Substation: One new transmission-level substation and modifications to the existing Cos Cob Substation
  • Siting review by: The Connecticut Siting Council (CSC)
  • Application filing to the CSC: June 26, 2015
  • CSC Decision issued: November 9, 2017
  • Cos Cob Substation start of modifications: May 12, 2018
  • Start of preparation for warehouse building demolition and pre-construction site preparation for Greenwich Substation: September 12, 2018
  • Start of construction for the new underground transmission lines: April 1, 2019
  • Start of warehouse building demolition for Greenwich Substation: April 1, 2019
  • Start of construction of the new Greenwich Substation: July 29, 2019

Next Steps (estimated timetable, subject to change):

  • Estimated project completion: 2020


Following receipt of the CSC’s application approval, Eversource is required to submit construction plans, called Development & Management Plans (D&M Plans), to the CSC for its Decision before construction can begin. These plans include, but are not limited to, further design detail, final site plan, construction sequencing, traffic management plans, work hours and laydown/staging areas. There are multiple D&M Plans for this project.

On February 20, 2018, Eversource submitted the Cos Cob Substation D&M Plan to the CSC. The CSC issued its Decision on April 12, 2018.

On May 18, 2018, Eversource submitted the Greenwich Substation Warehouse Building Demolition and Pre-Construction Site Preparation D&M Plan to the CSC. The CSC issued its Decision on June 21, 2018.

On October 3, 2018, Eversource submitted the Greenwich 115-kV Underground Transmission Lines D&M Plan to the CSC. The CSC issued its Decision on the D&M Plan for the underground transmission lines on January 17, 2019, including the following eight appendices: 

On February 4, 2019, Eversource submitted the Greenwich Substation Construction D&M Plan to the CSC. The CSC issued its Decision on the D&M Plan for the Greenwich Substation on March 29, 2019, including the following seven appendices:

On May 3, 2019, Eversource submitted the Indian Harbor Crossing D&M Plan for the 115-kV Double-Circuit Underground Transmission Lines to the CSC. The CSC issued its Decision on May 24, 2019, including the following seven appendices:


First, please know that Eversource takes every safety precaution while working in local communities, and that all people working on the construction project carry identification.

Please note that the project work will not interrupt electric service to homes or businesses.

Eversource is committed to updating neighbors, businesses and the community about project activities, especially during construction. Public outreach and coordination with the Town of Greenwich is ongoing throughout the project. Eversource representatives will occasionally go door-to-door to communicate with neighbors about the nearby construction project. They may leave an informational doorhanger at a home or business or knock on the door to provide an update on project work.

Construction will take place in phases. Work may occur in several locations along the project route at the same time, and work hours will be location-specific. Please refer to the Traffic Management Plan (TMP) for detailed information on work hours.

The sections below feature construction updates for both substations and the new underground transmission line. As construction progresses, this section will be updated with information for each street affected by construction of the underground lines. Please keep in mind that the construction schedule is approximate and may change. Due to weather or other circumstances, from time to time the crews may need to work longer hours or work on a Sunday.

Modifications to the Cos Cob Substation began in May 2018 and will continue through early 2020.

Work activities within the existing substation property include replacing the chain-link fence and installing underground electric lines inside the recently installed duct banks and splice vaults. Work completed to date includes vegetation removal; grading, digging and trenching; installation of new equipment and retaining walls; and restoration of areas disturbed by the work.

Work hours will typically be 7 a.m. to 6 p.m., Monday through Friday, and 9 a.m. to 5 p.m. on Saturdays.

Construction of the new 115-kV underground transmission line began the week of April 1, 2019. We anticipate that it will be complete in summer 2020.

Week of July 12, 2020:  

Day Work:

  • Woods Road:  Woods Road remains closed in accordance with Detour Plan 6. The work hours are 7 a.m. to 6 p.m., Monday through Friday, and 9 a.m. to 5 p.m. on Saturdays.
  • Indian Harbor Crossing: Crews will continue to complete the construction of the pedestrian bridge and the installation of duct bank at the Indian Harbor Crossing on Davis Avenue. The work hours are 7 a.m. to 6 p.m., Monday through Friday and 9 a.m. to 5 p.m. on Saturdays.
  • Indian Harbor Drive: Restoration activities, including curb installation will continue on Indian Harbor Drive. The work hours are 7 a.m. to 6 p.m., Monday through Friday and 9 a.m. to 5 p.m. on Saturdays with a single lane closure and alternating traffic around the work area.

Night Work: 

  • Arch Street: Excavation, rock removal and duct bank installation will continue in Arch Street between the I-95 Exit 3 ramps and Railroad Avenue. This work will be done at night, Sunday through Thursday, from 9 p.m. to 5 a.m., with a single lane closure and an alternating traffic pattern around the work areas.

Deliveries and equipment assembly will continue between the hours of 7 a.m. and 6 p.m., Monday through Friday and 9 a.m. to 5 p.m. on Saturdays. At times, Field Point Road may be closed between Railroad Avenue and Prospect Street within the work hours in accordance with Substation Detour Plan 1 to support the substation construction.

The construction of the permanent brick façade perimeter is now complete. Landscaping activities around the substation wall will continue over the next several weeks.

We anticipate construction of the new substation will be complete by the end of summer 2020.


Working in consultation with town and state officials, including the Connecticut Department of Transportation, Eversource has developed a Traffic Management Plan (TMP) for construction of the Greenwich Substation and Line Project.

The TMP includes hours of construction, area-specific traffic controls and detour plans for each segment of the underground line route.

Some of the files below are large in size and might take some time to load or download. Please note, detour plans are subject to change and may be updated.


Beginning with municipal briefings and other community outreach efforts, Eversource engages the community throughout the lifecycle of a project to provide information, answer questions and listen to concerns.

As the project proceeds through construction, Eversource is committed to updating neighbors, businesses, and the Greenwich community about construction activities in the area. 

If you would like to receive weekly email updates about the project's progress, please contact us at to subscribe.


For more information about the Greenwich Substation and Line Project, please email or call 800-793-2202.