News & Insights

Undergrounding: The Hidden Helper of Disaster Prep

Undergrounding power lines before and after
Kevin Schanen, P.E.

Kevin Schanen, P.E.

Undergrounding Practice Leader

The next time your lights stay on after a raging thunderstorm, ice storm, or wildfire, it may be from what you don’t see.

Electric utilities across the country are undertaking what the industry calls “undergrounding.” The simple definition means to bury overhead power lines underground. The complex reality of the process, however, takes years to accomplish through the performance of many steps:

  • Evaluating technical feasibility
  • Determining a funding mechanism
  • Performing a survey of the impacted area and investigating the locations of existing utilities
  • Preparing a design
  • Securing any necessary easements
  • Permitting
  • Selecting a contractor to install the new system in the built environment
  • Energizing the new system while keeping the existing overhead system in operation
  • Converting customer connections from the overhead system to the new underground system
Downed power lines laying across a residential street
Downed Power Lines from Hurricane Ian

Undergrounding most recently appeared in national news in the aftermath of Hurricane Ian. Florida Power & Light (FP&L), Florida’s largest utility, has buried about 40% of its distribution lines as part of a multi-billion-dollar resiliency effort. FP&L said neighborhoods with underground wires performed better than overhead wires during Ian.

Exhibit A in the performance of underground power is the Babcock Ranch community, which Kimley-Horn helped design, just east of Ft. Myers. It never lost electricity, in part due to underground power built from the start of the development.

This long-term investment in strengthening the grid with underground power lines is backed up with stellar performance data published by Florida’s Public Service Commission. FP&L’s 2021 Annual Reliability Report includes overhead versus underground power line comparisons. It also compares hybrid systems that include both types of power lines. FP&L reported that its underground power systems experienced half the interruptions of its hybrid systems and a third of the interruptions of overhead systems.

FP&L also calculates the Momentary Average Interruption Event, a common industry metric. It divides all customer momentary interruption events by the total number of customers served. A lower number means fewer interruptions per customer.

A momentary interruption is the type of interruption that makes you reset your clocks but is not considered a true outage.

2017-2021 Momentary Interruption Events Per Customer: Overhead vs. Underground

Overhead Power Lines Underground Power Lines Underground Improvement
2017
5.1
0.9
5.6 times better
2018
5.0
1.0
5.0 times better
2019
3.4
0.9
3.8 times better
2020
3.6
1.0
3.6 times better
2021
2.7
0.7
3.9 times better

The table illustrates two key facts:

  1. FP&L’s continued overhead infrastructure-hardening investment is significantly improving reliability.
  2. Underground power is still significantly more reliable than overhead power.

Beyond Resiliency and Reliability

Undergrounding projects also carry safety and aesthetic benefits. Many early U.S. undergrounding projects were primarily driven by community beautification initiatives. Today’s new residential and commercial developments almost always have underground power and communication systems, either by developer choice or municipal mandate. Landscape options increase when overhead power lines do not limit vertical growth. Plus, scenic vistas open up without obstructions from utility poles and lines.

From a safety perspective, humans and animals are far less likely to contact electrified lines when they are underground. Communities have stringent requirements to “call before you dig” to protect residents and workers from contacting underground power lines. However, every year people are electrocuted when trimming trees around overhead power lines. Additionally, toppled overhead power lines can create a hazard until the utility owner can safely de-energize them and restore them.

It’s Not Just Florida That Benefits From Underground Power Lines

While Hurricane Ian has recent headlines, utilities across America have been investing in undergrounding power lines for years. For example, in 1970, the City of San Diego began a program to convert all its power lines underground. It estimates another 54 years to complete the process for all residential power lines. Last year, Hilton Head, South Carolina completed a 17-year program to convert 115 miles of overhead power lines underground. In September, California’s governor signed SB 884, which will accelerate the placement of power lines underground to mitigate the risk of forest fires.

Funding for these types of projects largely depends on fees added to customers’ utility bills. Local projects initiated by the community can also be funded through special assessments or local capital improvement programs.

Undergrounding process to bury power lines
Directional Boring
Open trench undergrounding process
Open Cut Trench

Thanks to the proven performance of undergrounding, the federal government also has resiliency grant programs to help local communities fund their projects. The Federal Emergency Management Agency (FEMA) has helped to fund undergrounding through two programs.

  • The Hazard Mitigation Grant Program (HMGP) helps governments “develop hazard mitigation plans and rebuild in a way that reduces, or mitigates, future disaster losses in their communities.” FEMA can distribute money after a presidentially declared disaster. Utilities have used grants to bury power lines that were above ground before a disaster brought them down. The Town of Palm Beach, Florida secured an $8.5 million grant to partially fund one of the phases of its undergrounding program through HMGP funding tied to Hurricane Irma.
  • The Building Resilient Infrastructure and Communities (BRIC) program supports governments “as they undertake hazard mitigation projects, reducing the risks they face from disasters and natural hazards.” Unlike HMGP, communities can apply before disaster hits. BRIC offers funding up to a limit of 75% of a project’s cost.

These FEMA programs have helped to bury power lines in:

  • South Dakota that fell in a 1996 ice storm. The underground power lines survived severe weather unscathed in 2001, 2005, 2006, 2007 and 2008.
  • Alaska taken down by an avalanche. The underground work dug through both rock and glacial till.
  • Minnesota after ice-coated trees fell on the overhead power lines.
  • Idaho that were knocked out by a 2015 windstorm. The work covered 50 miles and encompassed 24 projects over a four-year period.

Additionally, the new Grid Hardening State/Tribal Formula Grant Program “is designed to strengthen and modernize America’s power grid against wildfires, extreme weather, and other natural disasters that are exacerbated by the climate crisis.” The federal government will distribute up to $2.3 billion in funding, and grant applications are due by March 31, 2023.

Cost and Value of Undergrounding Power Lines

In Kimley-Horn’s experience, undergrounding in the built environment can cost $3 million to $5 million per mile, including the cost of aerial communication cables. Some projects can cost less, and others may cost more, depending on the system and environment.

The complexity of converting overhead wires to underground locations requires more planning, stakeholder coordination, time to install, and specialized equipment than overhead infrastructure installation. But as the data shows, the investments are well worth the effort for both the customer and the utility owner.

Most importantly, the community benefits from underground power systems’ increased safety, reliability, aesthetics, and resiliency. These tangible benefits improve daily life and save lives during and after disasters.

So, the next time your home and local businesses weather a storm with continued power service, look up. If you don’t see power lines, an undergrounding project may be to thank.

About the Author

Kevin Schanen, P.E.

Kevin Schanen, P.E.

Kevin has nearly 25 years of diverse engineering and project management experience. He is the consultant project manager for the largest municipal undergrounding project currently underway in the state of Florida, as well as many other community undergrounding projects.

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