Among the questions raised about the proposed Rockdale - West Middleton project since it was introduced in 2005 is the possibility of constructing all or portions of the prooposed line underground.

Underground route map (pdf)

Compare cost of overhead to underground

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ATC's position and response

It is ATC's general practice is to place high voltage transmission lines on overhead structures. The issue of undergrounding a 345-kilovolt transmission line is complex. While there are aestetic benefits of placing transmission lines underground, those benefits are offset by some drawbacks including operation, maintenance and cost. The results of a feasibility/constructability study conducted by a Chicago-based engineernig firm that specilizes in the construction of underground facilities is included in ATC's construction application to the Public Service Commission of Wisconsin. However, ATC is not be recommending underground construction.

What was studied?

Because there are no 345-kV lines underground in Wisconsin, it was necessary for ATC to do a thorough examination of underground construction in response to requests from the PSC and local units of government.  In evaluating an underground option for a 345-kV project the scale and magnitude of the Rockdale - West Middleton project, the company needed to determine: (1) Whether or not a route exists that is suitable for underground construction and (2) The impacts on the cost and schedule (3) The operational performance of an underground line within the overall ATC network.

Why was undergrounding studied if ATC isn't proposing it?

At ATC, it is our obligation to explore any and all viable options and alternatives to the project we are proposing to ensure that the project proposal is the right system solution to the electrical problem we’re trying to solve. The PSC and a number of local units of government requested that ATC explore the feasibility of constructing the proposed line underground, particularly along areas of Madison’s Beltline highway and portions of Fitchburg. This study is a responsible and responsive approach to this request. The study provides valuable information to both supporters and opponents of undergrounding because it offers a comprehensive analysis of the challenges associated with this option, and allows the PSC to make a decision based on a full and complete evaluation of undergrounding. ATC does not believe the findings support a change in our position that overhead lines are the best option for this project. The PSC ultimately makes the decision; if a requirement is made to place portions of the line underground, ATC will comply. Learn more about underground construction.

The Beltline highway versus frontage and arterial roads
Among the routes being considered for an overhead transmission line is a route along the Beltline highway. Although the Beltline is a reasonable route option for an overhead line, it is not a viable route for an underground route primarily because of the construction methods used for underground facilities. The volume and speed of traffic, space requirements, truck and crew access, drainage and over/underpasses make major highways and interstate highways poor candidates for underground construction. Underground construction is generally limited to city streets, frontage roads and arterial streets, where adequate space is available to put traffic restrictions in place and meet the design and engineering requirements for an underground line.

For these reasons, separate and distinct underground route options were identified for the Rockdale - West Middleton Project. The route is characterized by four segments to allow the PSC to review the challenges and issues associated with different areas of the route. ATC is not recommending to the PSC the underground route or any underground facilities in its project application.

At a glance: overhead transmission lines vs. underground lines

(Click image to see larger version)