Choosing the optimal route for an electric transmission line can be complex. To be effective, the team involved should establish a comprehensive, methodical process.

This process often begins by identifying project objectives and utility preferences. These help to inform initial route selection decisions, such as whether to use an existing corridor. An upfront and proactive assessment of existing corridors — transmission lines, pipelines, roads, railroads, etc. — may be critical to long-term project success.

Feasibility of Using Existing Corridors

The use of existing corridors will have benefits and disadvantages unique to every project. The public, along with other key project stakeholders, often favors using an existing corridor when it’s available and feasible. Therefore, existing corridors should be considered in the initial route selection process.

Following the identification of a study area and data collection efforts, a constraint map is typically created that helps identify areas a route must avoid. In addition to identifying constraints, routing teams should also evaluate the feasibility of using existing corridors. An existing corridor should generally run in a direction that is beneficial to the new project, and the project team should identify and engage with corridor owners to determine whether the corridor can be used.

The two most common scenarios for using an existing corridor include constructing within or parallel to an existing right-of-way. Constructing within an existing right-of-way is often chosen when a transmission line is being rebuilt or upgraded or if there is enough space within the existing corridor to construct another transmission line.

This often results in the least amount of environmental and social impact because the corridor is already disturbed. It also eliminates the need to create any further fragmentation associated with an additional corridor and can reduce the degree of impacts to environmental resources, such as wooded areas.

A transmission line that parallels an existing right-of-way will usually share portions of the right-of-way if feasible, so that there is not entirely new disturbance by the project. This approach will still likely require some clearing; however, the overlap could help minimize environmental impacts, land use impacts and project costs.

Key Considerations for Routing

Before deciding on whether an existing corridor is the right option for your project, a team should consider:

  • Routing requirements. Review routing requirements for each local and/or state jurisdiction since requirements may vary by jurisdiction. Some states or counties specify that routes should run along lines of division, such as property lines or roads, while others have no requirements.
  • Encroachments within a right-of-way. An existing right-of-way could be riddled with encroachments. These encroachments create safety hazards, jeopardize a utility’s claim to its rights and can impact the construction effort. Encroachments would need to be identified and resolved with property owners first.
  • Visual impacts of the new line. While transmission line upgrades are ideal cases for using existing corridors, it is possible that a new transmission line will be a significant upgrade in infrastructure. What was once a wooden pole could soon be a large steel structure that might require additional right-of-way and would change the visual impact.
  • Reliability concerns. When a transmission line is placed adjacent to another transmission line, there could be increased reliability risks. For example, an extreme weather event could potentially take out both transmission lines at the same time.
  • Age of the existing corridor. Some existing corridors may have obtained rights-of-way several decades ago. When seeking to utilize this corridor today, there may be new requirements to account for that did not exist when the right-of-way was originally established.
  • Future expansion and development. When paralleling an existing corridor, such as a road, research should be conducted to identify if there are plans to change the corridor in the future, such as a road expansion, which may impact the ability to parallel a corridor.
  • Ownership of the existing corridor. Some corridors, such as an existing transmission line corridor, may be owned by a different utility and therefore may not allow for corridor sharing.

Regardless of regulations, preferences or environment, a documented route selection process that evaluates potential existing corridors is essential as projects progress and stakeholders build an understanding around why a route was selected.  


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Chris is a principal and department manager for environmental studies at Burns & McDonnell. He has over 26 years of experience and specializes in transmission line routing, site selection studies, permitting and other environmental projects across the country.