By Phyllis Turner, RLT Consulting Group
The use of geographic information systems (GIS) in the electric utility industry took a leap forward in 2006 with the Electric Power Research Institute’s (EPRI’s) publication of a new methodology for siting transmission lines.
Click here to enlarge image
Developed through a $500,000 tailored-collaboration project co-funded by EPRI, Georgia Transmission Corp. (GTC) and Photo Science, a Kentucky-based geospatial solutions company, the EPRI-GTC Siting Methodology was designed to address the ever-present and growing controversy over siting new transmission lines.
The use of GIS technology to site transmission lines is not new, nor is the use of a public involvement process. However, the EPRI-GTC methodology improves on these tools in significant ways. It combines an enterprise GIS software program and statistically sound algorithms with a more effective and transparent public process to enable utility professionals to make siting decisions that are more quantifiable, consistent and defensible.
“From our own experience facing highly organized opposition to new power lines, we concluded that there had to be a better way,” said Jerry Donovan, senior vice president of project services at GTC.
Georgia Transmission builds about 100 miles of new transmission line a year for the state’s electric cooperatives, which serve about 4 million people. After using the methodology to route more than 200 miles of transmission line, GTC is pleased with the results.
“In addition to more credible and transparent siting decisions, the methodology improved analytical capabilities and lowered data acquisition costs,” Donovan said. An analysis of eight projects found an average data-collection savings of 60 percent. Cost savings on individual projects ranged from $12,000 for a smaller project to more than $130,000 for larger projects. These savings are in addition to improvements in site selection and project scheduling.
Donovan said his company worked with EPRI to develop the methodology because GTC saw a need for a national model for siting transmission lines. Thousands of miles of new high-voltage transmission lines will be needed in the United States in the next decade to keep pace with demand. However, routing lines has become increasingly difficult because of public, political, legal and regulatory scrutiny. Electric utilities are sometimes criticized for leaving consumers out of the decision-making process, for making what often seemed to outsiders as arbitrary decisions, and for relying too heavily on the power of eminent domain to acquire property along preferred routes, Donovan said.
“While it is not a political panacea, our methodology does produce more consistent, defensible and transparent siting decisions,” he said. “Equally important, an objective, consistent national model gives utilities and regulatory agencies alike something to hang their hat on.”
More than 200 participants from government agencies, utilities, environmental groups and neighborhood organizations took part in research and development on the methodology, which was recently praised by the Kentucky Public Service Commission (PSC). After turning down previous requests, the Kentucky PSC approved an east Kentucky transmission line project using the EPRI-GTC Methodology.
Donovan pointed out three characteristics that differentiate the EPRI-GTC Siting Methodology from other siting methods that use GIS technology:
- External stakeholder input to calibrate the siting model;
- Standardized alternative perspectives; and,
- Computer algorithms help identify route alternatives.
The utility team and external stakeholders collaborate to assess and rank criteria for siting. The EPRI-GTC process standardizes alternative corridors. Algorithms create alternative corridors based on four categories: (1) built environment, protecting human and cultural resource areas; (2) natural environment, protecting plants, animals and aquatic resources; (3) engineering requirements, maximizing co-location and minimizing cost and schedule challenges; and (4) a simple average, a composite of the other three.
The Corridor Analyst software, which was developed and licensed by Photo Science, significantly improves productivity by:
- Assigning a numerical suitability value to all mapped features in the study area through an intuitive interface;
- Easily modifying the suitability values based on public input or unique environmental factors;
- Assigning engineering constraints, such as right of way width, maximum turn angle, and minimum run length;
- Creating a composite suitability map of the study area;
- Generating new corridor alternatives using constrained least-cost-path algorithms;
- Automatically generating alternative corridor reports, including statistics such as total length, number of landowners impacted, number of streams crossed, acreages of land use/land cover impacted, number of houses within a specified distance, etc.; and,
- Automatically generating reports summarizing criteria used.
The EPRI-GTC methodology is a four-step process that incorporates external stakeholder input, uses GIS technology to synthesize and quantify extensive amounts of data, and ultimately relies on the expert judgment of utility professionals to select a preferred route.
Step One: Identify Macro Corridors
First, the planning staff identifies beginning and end points where a new power line is needed. Satellite imagery and data on roads, terrain and existing transmission lines are merged to form one digital map of the study area. This map consists of a grid of 100 square-foot cells.
Each cell on the map is ranked. Features such as residential land use, agriculture and wetlands are ranked from 1 (most suitable) to 9 (least suitable). Using the cell values, a computer algorithm calculates optimal paths for three types of suitability surfaces:
- Locating with existing transmission lines,
- Locating with existing road rights of way, and,
- Crossing less developed areas.
The optimal paths are identified as macro corridors. Combined, the outer boundaries of the macro corridors define the study area.
Step Two: Identify Alternative Corridors
More detailed data (including aerial photography, detailed land use/land cover, buildings, etc.) are collected to identify alternative corridors within the macro corridors. Using suitability maps consisting of 15 square-foot cells, the four types of alternative corridors are defined.
The utility team and external stakeholders set evaluation criteria and rank factors, such as housing density, wetlands and land cover.
Stakeholders from government and industry and from civic, homeowner, environmental and other interest groups are invited to participate in ranking these factors. External stakeholder calibration can be done on a regional, statewide, and local basis. GTC and EPRI conducted these stakeholder meetings during the beginning stages of developing the methodology.
Step Three: Identify Alternative Routes
Within the alternative corridors, property lines are identified and buildings, which are digitized earlier in the process, are classified by type, such as occupied house, commercial building or industrial building. Collecting detailed data after alternative corridors are identified significantly reduces data acquisition costs.
In this phase, utility professionals use their expert judgment to identify alternative routes within the corridors defined by stakeholders.
Step Four: Select Preferred Route
GIS tools automatically calculate a standardized list of metrics for the alternative routes. Examples of data evaluated include cost, number of houses close to the route, acres of forest in right of way, etc. The alternative route evaluation tool uses data to filter out the top few routes to forward to the expert judgment tool.
Using the expert judgment tool, the utility siting team assigns relative weights to community concerns, visual concerns, special permit issues, scheduling risks and construction and maintenance accessibility. Then the top route alternatives are ranked using expert analysis to identify a preferred route.
Throughout the process, GIS is a productivity tool to aid experts in making more informed, objective and defensible decisions.
GTC is offering support to other utilities that would like to adopt the methodology. For more information, interested utility representatives can contact GTC at (770) 270-7050 or via email at EPRI-GTCSiting@gatrans.com.
Phyllis Turner is President of RLT Consulting Group, LLC, www.rltgroup.com. She has 15 years experience in public policy with respect to siting electric transmission lines.